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  • 1.
    Abdeldaim, Aly H.
    et al.
    Chalmers Univ Technol, Dept Chem & Chem Engn, Energy & Mat, SE-41296 Gothenburg, Sweden;Univ Liverpool, Dept Chem, 51 Oxford St, Oxford L7 3NY, Merseyside, England;Univ Liverpool, Mat Innovat Factory, 51 Oxford St, Oxford L7 3NY, Merseyside, England;Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Badrtdinov, Danis, I
    Ural Fed Univ, Theoret Phys & Appl Math Dept, Ekaterinburg 620002, Russia.
    Gibbs, Alexandra S.
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Manuel, Pascal
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Walker, Helen C.
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Le, Manh Duc
    Wu, Chien Hung
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Wardecki, Dariusz
    Chalmers Univ Technol, Dept Chem & Chem Engn, Energy & Mat, SE-41296 Gothenburg, Sweden.
    Eriksson, Sten-Gunnar
    Chalmers Univ Technol, Dept Chem & Chem Engn, Energy & Mat, SE-41296 Gothenburg, Sweden.
    Kvashnin, Yaroslav
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Tsirlin, Alexander A.
    Ural Fed Univ, Theoret Phys & Appl Math Dept, Ekaterinburg 620002, Russia;Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Expt Phys 6, D-86135 Augsburg, Germany.
    Nilsen, Göran J.
    Sci & Technol Facil Council, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England.
    Large easy-axis anisotropy in the one-dimensional magnet BaMo(PO4)(2)2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 21, artikkel-id 214427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present an extensive experimental and theoretical study on the low-temperature magnetic properties of the monoclinic anhydrous alum compound BaMo(PO4)(2). The magnetic susceptibility reveals strong antiferromagnetic interactions theta(CW) = -167 K and long-range magnetic order at T-N = 22 K, in agreement with a recent report. Powder neutron diffraction furthermore shows that the order is collinear, with the moments near the ac plane. Neutron spectroscopy reveals a large excitation gap Delta = 15 meV in the low-temperature ordered phase, suggesting a much larger easy-axis spin anisotropy than anticipated. However, the large anisotropy justifies the relatively high ordered moment, Neel temperature, and collinear order observed experimentally and is furthermore reproduced in a first-principles calculations by using a new computational scheme. We therefore propose BaMo(PO4)(2) to host S = 1 antiferromagnetic chains with large easy-axis anisotropy, which has been theoretically predicted to realize novel excitation continua.

  • 2.
    Abdel-Hafiez, Mahmoud
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik. Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China;Harvard Univ, Lyman Lab Phys, Cambridge, MA 02138 USA;Natl Univ Sci & Technol MISiS, Moscow 119049, Russia.
    Thiyagarajan, R.
    Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China.
    Majumdar, Arnab
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Luo, Wei
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Vasiliev, A. N.
    Natl Univ Sci & Technol MISiS, Moscow 119049, Russia;Natl Res South Ural State Univ, Chelyabinsk 454080, Russia;Moscow MV Lomonosov State Univ, Moscow 119991, Russia.
    Maarouf, A. A.
    Imam Abdulrahman Bin Faisal Univ, Inst Res & Med Consultat, Dept Phys, Dammam 31441, Saudi Arabia.
    Zybtsev, S. G.
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    Pokrovskii, V. Ya
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    V-Zaitsev-Zotov, S.
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    Pavlovskiy, V. V.
    RAS, Inst Radioengn & Elect, Moscow 125009, Russia.
    Pai, Woei Wu
    Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 106, Taiwan;Natl Taiwan Univ, Dept Phys, Taipei 10610, Taiwan.
    Yang, W.
    Ctr High Pressure Sci & Technol Adv Res, Shanghai 201203, Peoples R China.
    Kulik, L. , V
    Pressure-induced reentrant transition in NbS3 phases: Combined Raman scattering and x-ray diffraction study2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 23, artikkel-id 235126Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the evolution of charge density wave states under pressure for two NbS3 phases: triclinic (phase I) and monoclinic (phase II) at room temperature. Raman and x-ray diffraction (XRD) techniques are applied. The x-ray studies on the monoclinic phase under pressure show a compression of the lattice at different rates below and above similar to 7 GPa but without a change in space group symmetry. The Raman spectra of the two phases evolve similarly with pressure; all peaks almost disappear in the similar to 6-8 GPa range, indicating a transition from an insulating to a metallic state, and peaks at new positions appear above 8 GPa. The results suggest suppression of the ambient charge-density waves and their subsequent recovery with new orderings above 8 GPa.

  • 3.
    Akansel, Serkan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Kumar, Ankit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Behera, Nilamani
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Husain, Sajid
    Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
    Brucas, Rimantas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Chaudhary, Sujeet
    Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Thickness dependent enhancement of damping in Co2FeAl/β-Ta thin films2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 13, artikkel-id 134421Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present work Co2FeAl (CFA) thin films were deposited by ion beam sputtering on Si (100) substrates at the optimized deposition temperature of 300°C. A series of CFA films with different thickness (tCFA ); 8, 10, 12, 14, 16, 18 and 20 nm were prepared and all samples were capped with a 5 nm thick b-Ta layer. The thickness dependent static and dynamic properties of the films were studied by SQUID magnetometry, in-plane as well as out-of-plane broadband VNA-FMR measurements and angle dependent cavity FMR measurements. The saturation magnetization and the coercive field were found to be weakly thickness dependent and lie in the range 900 – 950 kA/m and 0.53 – 0.87 kA/m, respectively. The effective damping parameter ( αeff) extracted from in-plane and out-of-plane FMR results reveal a 1/tCFA dependence, the values for the in-plane αeff being larger due to two-magnon scattering (TMS). The origin of the αeff thickness dependence is spin pumping into the non-magnetic b-Ta layer and in case of the in-plane  αeff also a thickness dependent TMS contribution. From the out-of-plane FMR results, it was possible to disentangle the different contributions to αeff   and to the extract values for the intrinsic Gilbert damping (αG ) and the effective spin-mixing conductance (g_eff^↑↓ ) of the CFA/ b-Ta interface, yielding αG=1.1X10-3 and g_eff^↑↓=2.90x1019 m-2.

  • 4.
    Akansel, Serkan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Kumar, Ankit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Venugopal, Vijayaharan A.
    Seagate Technol, Londonderry BT48 0BF, North Ireland.
    Esteban-Puyuelo, Raquel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Banerjee, Rudra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Autieri, Carmine
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Brucas, Rimantas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Behera, Nilamani
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Sortica, Mauricio A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Primetzhofer, Daniel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Tillämpad kärnfysik.
    Basu, Swaraj
    Seagate Technol, Londonderry BT48 0BF, North Ireland.
    Gubbins, Mark A.
    Seagate Technol, Londonderry BT48 0BF, North Ireland.
    Sanyal, Biplab
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Enhanced Gilbert damping in Re-doped FeCo films: Combined experimental and theoretical study2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 17, artikkel-id 174408Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of rhenium doping in the range 0-10 at.% on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first-principles electronic structure calculations focusing on the change of the saturation magnetization (M-s) and the Gilbert damping parameter (alpha). Both experimental and theoretical results show that M-s decreases with increasing Re-doping level, while at the same time alpha increases. The experimental low temperature saturation magnetic induction exhibits a 29% decrease, from 2.31 to 1.64 T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 2.1 x 10(-3), which is close to the theoretically calculated Gilbert damping parameter. With 10 at.% Re doping, the damping parameter increases to 7.8 x 10(-3), which is in good agreement with the theoretical value of 7.3 x 10(-3). The increase in damping parameter with Re doping is explained by the increase in the density of states at the Fermi level, mostly contributed by the spin-up channel of Re. Moreover, both experimental and theoretical values for the damping parameter weakly decrease with decreasing temperature.

  • 5.
    Albaalbaky, Ahmed
    et al.
    Normandie Univ, UNIROUEN, CNRS, INSA Rouen,GPM, St Etienne Du Rouvray, France..
    Kvashnin, Yaroslav
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ledue, Denis
    Normandie Univ, UNIROUEN, CNRS, INSA Rouen,GPM, St Etienne Du Rouvray, France..
    Patte, Renaud
    Normandie Univ, UNIROUEN, CNRS, INSA Rouen,GPM, St Etienne Du Rouvray, France..
    Fresard, Raymond
    Normandie Univ, UNICAEN, ENSICAEN, CNRS,CRISMAT, F-14050 Caen, France..
    Magnetoelectric properties of multiferroic CuCrO2 studied by means of ab initio calculations and Monte Carlo simulations2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 6, artikkel-id 064431Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Motivated by the discovery of multiferroicity in the geometrically frustrated triangular antiferromagnet CuCrO2 below its Neel temperature T-N, we investigate its magnetic and ferroelectric properties using ab initio calculations and Monte Carlo simulations. Exchange interactions up to the third nearest neighbors in the ab plane, interlayer interaction, and single ion anisotropy constants in CuCrO2 are estimated by a series of density functional theory calculations. In particular, our results evidence a hard axis along the [110] direction due to the lattice distortion that takes place along this direction below T-N. Our Monte Carlo simulations indicate that the system possesses a Neel temperature T-N approximate to 27 K very close to the ones reported experimentally (T-N = 24-26 K). Also we show that the ground state is a proper-screw magnetic configuration with an incommensurate propagation vector pointing along the [110] direction. Moreover, our work reports the emergence of spin helicity below T-N which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model. We confirm the electric control of spin helicity by simulating P-E hysteresis loops at various temperatures.

  • 6.
    Albaalbaky, Ahmed
    et al.
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Kvashnin, Yaroslav
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Patte, Renaud
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Fresard, Raymond
    Normandie Univ, CRISMAT, CNRS, UNICAEN,ENSICAEN, F-14050 Caen, France.
    Ledue, Denis
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Effects of Ga doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2: Ab initio and Monte Carlo approaches2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 17, artikkel-id 174403Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of nonmagnetic impurity doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2 are investigated by means of density functional theory calculations and Monte Carlo simulations. Density functional theory calculations show that replacing up to 30% of Cr3+ ions by Ga3+ ones does not significantly affect the remaining Cr-Cr superexchange interactions. Monte Carlo simulations show that CuCr1-xGaxO2 preserves its magnetoelectric properties up to x similar or equal to 0.15 with a spiral ordering, while it becomes disordered at higher fractions. Antiferromagnetic transition shifts towards lower temperatures with increasing x and eventually disappears at x >= 0.2. Our simulations show that Ga3+ doping increases the Curie-Weiss temperature of CuCr1-xGaxO2, which agrees well with experimental observations. Moreover, our results show that the incommensurate ground-state configuration is destabilized by Ga3+ doping under zero applied field associated with an increase of frustration. Finally, coupling between noncollinear magnetic ordering and electric field is reported for x <= 0.15 through simulating P-E hysteresis loops, which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model.

  • 7.
    Albaalbaky, Ahmed
    et al.
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Kvashnin, Yaroslav
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Patte, Renaud
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Ledue, Denis
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS,GPM, F-76800 St Etienne Du Rouvray, France.
    Analytical and numerical investigations of noncollinear magnetic ordering in the frustrated delafossite CuCrO22019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 10, artikkel-id 104415Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The magnetic propagation vector in delafossite CuCrO2 with classical Heisenberg spins is calculated analytically as a function of exchange interactions up to fourth-nearest neighbors. Exchange interactions are estimated by a series of density functional theory calculations for several values of lattice distortion. Our calculations show that the magnetic propagation vector is directly affected by the considered distortions providing different stable commensurate or incommensurate magnetic configurations. A realistic set of exchange interactions corresponding to a 0.1% lattice distortion yields the experimental ground state with an incommensurate propagation vector q similar to (0.329, 0.329, 0). We find that a very weak antiferromagnetic interlayer interaction favors an incommensurate ordering even in the absence of lattice distortion. Moreover, the exchange energy of a magnetic configuration of a finite crystal of CuCrO2 with periodic boundary conditions is derived analytically. Based on that, highly accurate Monte Carlo simulations performed on CuCrO2 confirm both the proposed analytical calculations and the density functional theory estimations, where we obtain excellent convergence toward the experimental ground state with a magnetic propagation vector q = (0.3288, 0.3288, 0).

  • 8.
    Andersson, Mikael Svante
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Mathieu, Roland
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Normile, Peter S.
    Univ Castilla La Mancha, Spain.
    Lee, Su Seong
    Inst Bioengn & Nanotechnol, Singapore.
    Singh, Gurvinder
    Norwegian Univ Sci & Technol NTNU, Dept Mat Sci & Engn, Norway.
    Nordblad, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    De Toro, José A.
    Univ Castilla La Mancha, Spain.
    Magnetic properties of nanoparticle compacts with controlled broadening of the particle size distribution2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 18, artikkel-id 184431Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Binary random compacts with different proportions of small (volume V) and large (volume 2V) essentially bare maghemite nanoparticles are used to investigate the effect of controllably broadening the particle size distribution on the magnetic properties of magnetic nanoparticle assemblies with strong dipolar interaction. A series of eight random mixtures of highly uniform 9.0- and 11.5-nm-diameter maghemite particles prepared by thermal decomposition is studied. In spite of the severely broadened size distributions in the mixed samples, well-defined superspin glass transition temperatures are observed across the series, their values increasing linearly with the weight fraction of large particles.

  • 9.
    Appelt, W. H.
    et al.
    Univ Augsburg, Inst Phys, Theoret Phys 2, D-86135 Augsburg, Germany;Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany.
    Östlin, A.
    Univ Augsburg, Ctr Elect Correlat & Magnetism, Inst Phys, Theoret Phys 3, D-86135 Augsburg, Germany.
    Di Marco, Igor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Asia Pacific Ctr Theoret Phys, Pohang 790784, Gyeonbuk, South Korea;POSTECH, Dept Phys, Pohang 790784, Gyeonbuk, South Korea.
    Leonov, I
    Inst Met Phys, Sofia Kovalevskaya St 18,GSP 170, Ekaterinburg 620219, Russia;Ural Fed Univ, Ekaterinburg 620002, Russia.
    Sekania, M.
    Univ Augsburg, Ctr Elect Correlat & Magnetism, Inst Phys, Theoret Phys 3, D-86135 Augsburg, Germany;Andronikashvili Inst Phys, Tamarashvili 6, GE-0177 Tbilisi, Georgia.
    Vollhardt, D.
    Univ Augsburg, Ctr Elect Correlat & Magnetism, Inst Phys, Theoret Phys 3, D-86135 Augsburg, Germany.
    Chioncel, L.
    Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany;Univ Augsburg, Ctr Elect Correlat & Magnetism, Inst Phys, Theoret Phys 3, D-86135 Augsburg, Germany.
    Lattice dynamics of palladium in the presence of electronic correlations2020Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, nr 7, artikkel-id 075120Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We compute the phonon dispersion, density of states, and the Gruneisen parameters of bulk palladium in the combined density functional theory (DFT) and dynamical mean-field theory. We find good agreement with experimental results for ground-state properties (equilibrium lattice parameter and bulk modulus) and the experimentally measured phonon spectra. We demonstrate that at temperatures T less than or similar to( )20 K the phonon frequency in the vicinity of the Kohn anomaly, omega(T1)(q(K)), strongly decreases. This is in contrast to DFT where this frequency remains essentially constant in the whole temperature range. Apparently, correlation effects reduce the restoring force of the ionic displacements at low temperatures, leading to a mode softening.

  • 10.
    Arapan, S.
    et al.
    VSB Tech Univ Ostrava, IT4Innovat, 17 Listopadu 2172-15, Ostrava 70800, Czech Republic.
    Nieves, P.
    VSB Tech Univ Ostrava, IT4Innovat, 17 Listopadu 2172-15, Ostrava 70800, Czech Republic;Univ Burgos, Int Res Ctr Crit Raw Mat & Adv Ind Technol, ICCRAM, Burgos 09001, Spain.
    Herper, Heike C.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Legut, D.
    VSB Tech Univ Ostrava, IT4Innovat, 17 Listopadu 2172-15, Ostrava 70800, Czech Republic;VSB Tech Univ Ostrava, Nanotechnol Ctr, 17 Listopadu 2172-15, Ostrava 70800, Czech Republic.
    Computational screening of Fe-Ta hard magnetic phases2020Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, nr 1, artikkel-id 014426Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we perform a systematic calculation of the Fe-Ta phase diagram to discover hard magnetic phases. By using structure prediction methods based on evolutionary algorithms, we identify two energetically stable magnetic structures: a tetragonal Fe3Ta (space group 122) and a cubic Fe5Ta (space group 216) binary phase. The tetragonal structure is estimated to have both high saturation magnetization (mu M-0(s) = 1.14 T) and magnetocrystalline anisotropy (K-1 = 2.17 MJ/m(3)) suitable for permanent magnet applications. The high-throughput screening of magnetocrystalline anisotropy also reveals two low-energy metastable hard magnetic phases: Fe5Ta2 (space group 156) and Fe6Ta (space group 194), that may exhibit intrinsic magnetic properties comparable to SmCo5 and Nd2Fe14B, respectively.

  • 11.
    Awoga, Oladunjoye A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Bouhon, Adrien
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Domain walls in a chiral d-wave superconductor on the honeycomb lattice2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 1, artikkel-id 014521Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We perform a fully self-consistent study of domain walls between different chiral domains in chiral d(x2-y2) +/- id(xy) -wave superconductors with an underlying honeycomb lattice structure. We investigate domain walls along all possible armchair and zigzag directions and with a finite global phase shift across the domain wall, in addition to the change of chirality. For armchair domain walls we find the lowest domain wall energy at zero global phase shift, while the most favorable zigzag domain wall has a finite global phase shift dependent on the doping level. Belowthe van Hove singularity the armchair domain wall is most favorable, while at even higher doping the zigzag domain wall has the lowest energy. The domain wall causes a local suppression of the superconducting order parameter, with the superconducting recovery length following a universal curve for all domain walls. Moreover, we always find four subgap states crossing zero energy and well localized to the domain wall. However, the details of their energy spectrum vary notably, especially with the global phase shift across the domain wall.

  • 12.
    Awoga, Oladunjoye
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Björnson, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Disorder robustness and protection of Majorana bound states in ferromagnetic chains on conventional superconductors2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 18, artikkel-id 184511Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Majorana bound states (MBSs) are well established in the clean limit in chains of ferromagnetically aligned impurities deposited on conventional superconductors with finite spin-orbit coupling. Here we show that these MBSs are very robust against disorder. By performing self-consistent calculations we find that the MBSs are protected as long as the surrounding superconductor show no large signs of inhomogeneity. We also find that longer chains offer more stability against disorder for the MBSs, albeit the minigap decreases, as do increasing strengths of spin-orbit coupling and superconductivity.

  • 13.
    Awoga, Oladunjoye
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Probing unconventional superconductivity in proximitized graphene by impurity scattering2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 21, artikkel-id 214515Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate how potential impurities are a very powerful tool for determining the pairing symmetry in graphene, proximity coupled to a spin-singlet superconductor. All d-wave states are characterized by subgap resonances, with spatial patterns clearly distinguishing between nodal and chiral d-wave symmetry, while s-wave states have no subgap resonances. We also find strong supergap impurity resonances associated with the normal state Dirac point. Subgap and supergap resonances only interact at very low doping levels, then causing suppression of the supergap resonances.

  • 14.
    Bagrov, Andrey A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Radboud Univ Nijmegen, Inst Mol & Mat, Heijndaalseweg 135, NL-6525 AJ Nijmegen, Netherlands.
    Guinea, Francisco
    IMDEA Nanosci, Calle Faraday 9, E-28049 Madrid, Spain;Univ Manchester, Sch Phys & Astron, Manchester M13 9PY, Lancs, England.
    Katsnelson, Mikhail, I
    Radboud Univ Nijmegen, Inst Mol & Mat, Heijndaalseweg 135, NL-6525 AJ Nijmegen, Netherlands.
    Suppressing backscattering of helical edge modes with a spin bath2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 19, artikkel-id 195426Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We address the question of stability of protected helical edge states at the boundary of two-dimensional topological insulators upon interactions with the external bath. We study how backscattering amplitude changes when different interaction channels between the system and the environment are present. Drawing an analogy with the concept of pointer states in theory of open quantum systems, we demonstrate that in a certain regime the interplay between the Coulomb and the spin-spin interactions can make the backscattering process strictly irrelevant, and the helical modes become robust states with a well-defined momentum. This opens a possibility to use the external spin bath as a stabilizer that alleviates destructive effects and restores the helicity protection.

  • 15.
    Barthel, J.
    et al.
    Rhein Westfal TH Aachen, Cent Facil Electron Microscopy, D-52074 Aachen, Germany.;Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Mayer, J.
    Rhein Westfal TH Aachen, Cent Facil Electron Microscopy, D-52074 Aachen, Germany.;Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Rusz, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ho, P. -L
    Beijing National Center for Electron Microscopy, Laboratory of Advanced Materials, The State Key Laboratory of New Ceramics and Fine Processing, and School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.; Central Facility for Electron Microscopy, RWTH Aachen University, 52074 Aachen, Germany.
    Zhong, X. Y.
    Tsinghua Univ, State Key Lab New Ceram & Fine Proc, Lab Adv Mat, Beijing Natl Ctr Electron Microscopy, Beijing 100084, Peoples R China.;Tsinghua Univ, Sch Mat Sci & Engn, Beijing 100084, Peoples R China..
    Lentzen, M.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Dunin-Borkowski, R. E.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Urban, K. W.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Brown, H. G.
    Monash Univ, Sch Phys & Astron, Clayton, Vic 3800, Australia..
    Findlay, S. D.
    Monash Univ, Sch Phys & Astron, Clayton, Vic 3800, Australia..
    Allen, L. J.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany.;Univ Melbourne, Sch Phys, Parkville, Vic 3010, Australia..
    Understanding electron magnetic circular dichroism in a transition potential approach2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 14, artikkel-id 144103Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper introduces an approach based on transition potentials for inelastic scattering to understand the underlying physics of electron magnetic circular dichroism (EMCD). The transition potentials are sufficiently localized to permit atomic-scale EMCD. Two-beam and three-beam systematic row cases are discussed in detail in terms of transition potentials for conventional transmission electron microscopy, and the basic symmetries which arise in the three-beam case are confirmed experimentally. Atomic-scale EMCD in scanning transmission electron microscopy (STEM), using both a standard STEM probe and vortex beams, is discussed.

  • 16.
    Bekaert, J.
    et al.
    Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
    Aperis, Alex
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Partoens, B.
    Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
    Oppeneer, Peter M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Milosevic, M. V.
    Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
    Advanced first-principles theory of superconductivity including both lattice vibrations and spin fluctuations: The case of FeB42018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 1, artikkel-id 014503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present an advanced method to study spin fluctuations in superconductors quantitatively and entirely fromfirst principles. This method can be generally applied to materials where electron-phonon coupling and spinfluctuations coexist. We employ it here to examine the recently synthesized superconductor iron tetraboride(FeB4) with experimentalTc∼2.4K[H.Gouet al.,Phys.Rev.Lett.111,157002(2013)]. We prove thatFeB4is particularly prone to ferromagnetic spin fluctuations due to the presence of iron, resulting in a largeStoner interaction strength,I=1.5 eV, as calculated from first principles. The other important factor is itsFermi surface that consists of three separate sheets, among which two are nested ellipsoids. The resultingsusceptibility has a ferromagnetic peak aroundq=0, from which we calculated the repulsive interaction betweenCooper pair electrons using the random phase approximation. Subsequently, we combined the electron-phononinteraction calculated from first principles with the spin fluctuation interaction in fully anisotropic Eliashbergtheory calculations. We show that the resulting superconducting gap spectrum is conventional, yet very stronglydepleted due to coupling to the spin fluctuations. The critical temperature decreases from Tc=41 K, if they arenot taken into account, toTc=1.7 K, in good agreement with the experimental value.

  • 17. Bekaert, J.
    et al.
    Aperis, Alex
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Partoens, B.
    Oppeneer, Peter M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Milošević, M. V.
    Evolution of multigap superconductivity in the atomically thin limit: Strain-enhanced three-gap superconductivity in monolayer MgB22017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, artikkel-id 094510Artikkel i tidsskrift (Fagfellevurdert)
  • 18.
    Bekaert, J.
    et al.
    Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Vercauteren, S.
    Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Aperis, Alex
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Komendova, Lucia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Prozorov, R.
    Iowa State Univ, Dept Phys & Astron, Ames, IA 50011 USA.;Iowa State Univ, Ames Lab, Ames, IA 50011 USA..
    Partoens, B.
    Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Milosevic, M. V.
    Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Anisotropic type-I superconductivity and anomalous superfluid density in OsB22016Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 14, artikkel-id 144506Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a microscopic study of superconductivity in OsB2, and discuss the origin and characteristic length scales of the superconducting state. From first-principles we show that OsB2 is characterized by three different Fermi sheets, and we prove that this fermiology complies with recent quantum-oscillation experiments. Using the found microscopic properties, and experimental data from the literature, we employ Ginzburg-Landau relations to reveal that OsB2 is a distinctly type-I superconductor with a very low Ginzburg-Landau parameter kappa-a rare property among compound materials. We show that the found coherence length and penetration depth corroborate the measured thermodynamic critical field. Moreover, our calculation of the superconducting gap structure using anisotropic Eliashberg theory and ab initio calculated electron-phonon interaction as input reveals a single but anisotropic gap. The calculated gap spectrum is shown to give an excellent account for the unconventional behavior of the superfluid density of OsB2 measured in experiments as a function of temperature. This reveals that gap anisotropy can explain such behavior, observed in several compounds, which was previously attributed solely to a two-gap nature of superconductivity.

  • 19.
    Bender, P.
    et al.
    Univ Cantabria, Fac Sci, Dept CITIMAC, E-39005 Santander, Spain;Univ Luxembourg, L-1511 Luxembourg, Grand Duchy Of, Luxembourg.
    Wetterskog, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Honecker, D.
    Inst Laue Langevin, F-38042 Grenoble, France.
    Fock, J.
    Tech Univ Denmark, DK-2800 Lyngby, Denmark.
    Frandsen, C.
    Tech Univ Denmark, DK-2800 Lyngby, Denmark.
    Moerland, C.
    Tech Univ Eindhoven, Dept Appl Phys, Eindhoven, Netherlands.
    Bogart, L. K.
    UCL, UCL Healthcare Biomagnet Lab, 21 Albemarle St, London W1S 4BS, England.
    Posth, O.
    Phys Tech Bundesanstalt, D-10587 Berlin, Germany.
    Szczerba, W.
    Bundesanstalt Mat Forsch & Prufung, D-12205 Berlin, Germany;AGH Univ Sci & Technol, PL-30059 Krakow, Poland.
    Gavilan, H.
    CSIC, ICMM, Madrid, Spain.
    Costo, R.
    CSIC, ICMM, Madrid, Spain.
    Fernandez-Diaz, M. T.
    Inst Laue Langevin, F-38042 Grenoble, France.
    Gonzalez-Alonso, D.
    Univ Cantabria, Fac Sci, Dept CITIMAC, E-39005 Santander, Spain;Univ Luxembourg, L-1511 Luxembourg, Grand Duchy Of, Luxembourg.
    Fernandez Barquin, L.
    Univ Cantabria, Fac Sci, Dept CITIMAC, E-39005 Santander, Spain;Univ Luxembourg, L-1511 Luxembourg, Grand Duchy Of, Luxembourg.
    Johansson, C.
    RISE Acreo, S-40014 Gothenburg, Sweden.
    Dipolar-coupled moment correlations in clusters of magnetic nanoparticles2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 22, artikkel-id 224420Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Here, we resolve the nature of the moment coupling between 10-nm dimercaptosuccinic acid-coated magnetic nanoparticles. The individual iron oxide cores were composed of >95 % maghemite and agglomerated to clusters. At room temperature the ensemble behaved as a superparamagnet according to Mossbauer and magnetization measurements, however, with clear signs of dipolar interactions. Analysis of temperature-dependent ac susceptibility data in the superparamagnetic regime indicates a tendency for dipolar-coupled anticorrelations of the core moments within the clusters. To resolve the directional correlations between the particle moments we performed polarized small-angle neutron scattering and determined the magnetic spin-flip cross section of the powder in low magnetic field at 300 K. We extract the underlying magnetic correlation function of the magnetization vector field by an indirect Fourier transform of the cross section. The correlation function suggests nonstochastic preferential alignment between neighboring moments despite thermal fluctuations, with anticorrelations clearly dominating for next-nearest moments. These tendencies are confirmed by Monte Carlo simulations of such core clusters.

  • 20.
    Berger, Andrew J.
    et al.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Edwards, Eric R. J.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Nembach, Hans T.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Karis, Olof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Weiler, Mathias
    Tech Univ Munich, Phys Dept, D-85748 Garching, Germany;Bayerische Akad Wissensch, Walther Meissner Inst, D-85748 Garching, Germany.
    Silva, T. J.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Determination of the spin Hall effect and the spin diffusion length of Pt from self-consistent fitting of damping enhancement and inverse spin-orbit torque measurements2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 2, artikkel-id 024402Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding the evolution of spin-orbit torque (SOT) with increasing heavy-metal thickness in ferromagnet/normal metal (FM/NM) bilayers is critical for the development of magnetic memory based on SOT. However, several experiments have revealed an apparent discrepancy between damping enhancement and dampinglike SOT regarding their dependence on NM thickness. Here, using linewidth and phase-resolved amplitude analysis of vector network analyzer ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extract damping enhancement and both fieldlike and dampinglike inverse SOT in Ni80Fe20/Pt bilayers as a function of Pt thickness. By enforcing an interpretation of the data which satisfies Onsager reciprocity, we find that both the damping enhancement and dampinglike inverse SOT can be described by a single spin diffusion length (approximate to 4nm), and that we can separate the spin pumping and spin-memory loss contributions to the total damping. This analysis indicates that less than 40% of the angular momentum pumped by FMR through the Ni80Fe20/Pt interface is transported as spin current into the Pt. On account of the spin-memory loss and corresponding reduction in total spin current available for spin-charge transduction in the Pt, we determine the Pt spin Hall conductivity [sigma(SH) = (2.36 +/- 0.04) x 10(6) omega(-1) m(-1)] and bulk spin Hall angle (theta(SH) = 0.387 +/- 0.008) to be larger than commonly cited values. These results suggest that Pt can be an extremely useful source of SOT if the FM/NM interface can be engineered to minimize spin loss. Lastly, we find that self-consistent fitting of the damping and SOT data is best achieved by a model with Elliott-Yafet spin relaxation and extrinsic inverse spin Hall effect, such that both the spin diffusion length and spin Hall conductivity are proportional to the Pt charge conductivity.

  • 21.
    Björnson, Kristofer
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Balatsky, Alexander V.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Superconducting order parameter π-phase shift in magnetic impurity wires2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 10, artikkel-id 104521Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It has previously been found that a magnetic impurity in a conventional s-wave superconductor can give rise to a local π-phase shift of the superconducting order parameter. By studying a finite wire of ferromagnetic impurities, we are able to trace the origin of the π-phase shift to a resonance condition for the Bogoliubov-de Gennes quasiparticle states. When non-resonating states localized at the impurity sites are pulled into the condensate for increasing magnetic strength, the superconducting order parameter is reduced in discrete steps, eventually resulting in a π-phase shift. We also show that for a finite spin-orbit coupling, the π-phase shift is preserved and occurs in a large portion of the topologically non-trivial phase.

  • 22.
    Björnson, Kristofer
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Univ Copenhagen, Niels Bohr Inst, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark..
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Probing chiral edge states in topological superconductors through spin-polarized local density of state measurements2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 14, artikkel-id 140504Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show that spin-polarized local density of states (LDOS) measurements can uniquely determine the chiral nature of topologically protected edge states surrounding a ferromagnetic island embedded in a conventional superconductor with spin-orbit coupling. The spin-polarized LDOS show a strong spin polarization directly tied to the normal direction of the edge with opposite polarizations on opposite sides of the island and with a distinct oscillatory pattern in energy.

  • 23.
    Bondarenko, N.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Kvashnin, Y.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Chico, J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Bergman, A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Eriksson, O.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Skorodumova, N. V.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Spin-polaron formation and magnetic state diagram in La-doped CaMnO32017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 22, artikkel-id 220401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    LaxCa1-xMnO3 (LCMO) has been studied in the framework of density functional theory (DFT) using Hubbard-U correction. We show that the formation of spin polarons of different configurations is possible in the G-type antiferromagnetic phase. We also show that the spin-polaron (SP) solutions are stabilized due to an interplay of magnetic and lattice effects at lower La concentrations and mostly due to the lattice contribution at larger concentrations. Our results indicate that the development of SPs is unfavorable in the C- and A-type antiferromagnetic phases. The theoretically obtained magnetic state diagram is in good agreement with previously reported experimental results.

  • 24.
    Bondarenko, Nina G.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Chico, J.
    Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75121 Uppsala, Sweden;Forschungszentrum Julich, Peter Grunberg Inst, D-52428 Julich, Germany;Forschungszentrum Julich, Inst Adv Simulat, D-52428 Julich, Germany;JARA, D-52428 Julich, Germany.
    Kvashnin, Yaroslav
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Bergman, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Univ Versailles, Univ Paris Sud, CNRS, Maison Simulat,CEA,INRIA,USR 3441, F-91191 Gif Sur Yvette, France;CEA, INAC MEM, L Sim, F-38000 Grenoble, France.
    Skorodumova, N. , V
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Örebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden.
    Spin polaronics: Static and dynamic properties of spin polarons in La-doped CaMnO42019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 13, artikkel-id 134443Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The static and dynamic properties of spin polarons in La-doped CaMnO3 are explored theoretically, by means of an effective low-energy Hamiltonian. All parameters of the effective Hamiltonian are evaluated from first-principles theory. The Hamiltonian is used to investigate the temperature stability as well as the response to an external applied electric field, for spin polarons in bulk, surface, and as single two-dimensional layers. Technically this involves atomistic spin-dynamics simulations in combination with kinetic Monte Carlo simulations. Where a comparison can be made, our simulations exhibit excellent agreement with available experimental data and previous theory. Remarkably, we find that excellent control of the mobility of spin polarons in this material can be achieved, and that the critical parameters deciding this are the temperature and strength of the applied electrical field. We outline different technological implications of spin polarons, and point to spin polaronics as an emerging subfield of nanotechnology. In particular, we demonstrate that it is feasible to write and erase information on an atomic scale, by use of spin polarons in CaMnO3.

  • 25.
    Borla, Umberto
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi. Tech Univ Munich, Dept Phys, D-85748 Garching, Germany..
    Kuzmanovski, Dushko
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Tuning Majorana zero modes with temperature in pi-phase Josephson junctions2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 1, artikkel-id 014507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study a superconductor-normal-state-superconductor Josephson junction along the edge of a quantum spin Hall insulator with a superconducting pi phase across the junction. We solve self-consistently for the superconducting order parameter and find both real junctions, where the order parameter is fully real throughout the system, and junctions where the order parameter has a complex phase winding. Real junctions host two Majorana zero modes (MZMs), while phase-winding junctions have no subgap states close to zero energy. At zero temperature we find that the phase-winding solution always has the lowest free energy, which we establish as being due to a strong proximity effect into the N region. With increasing temperature this proximity effect is dramatically decreased and we find a phase transition into a real junction with two MZMs.

  • 26.
    Borlenghi, Simone
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Mahani, M. R.
    Royal Inst Technol, Dept Mat & Nanophys, Sch Informat & Commun Technol, Electrum 229, SE-16440 Kista, Sweden..
    Delin, Anna
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Royal Inst Technol, Dept Mat & Nanophys, Sch Informat & Commun Technol, Electrum 229, SE-16440 Kista, Sweden.;KTH Royal Inst Technol, Swedish E Sci Res Ctr SeRC, SE-10044 Stockholm, Sweden..
    Fransson, Jonas
    Nanoscale control of heat and spin conduction in artificial spin chains2016Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 13, artikkel-id 134419Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We describe a mechanism to control the energy and magnetization currents in an artificial spin chain, consisting of an array of permalloy nanodisks coupled through a magnetodipolar interaction. The chain is kept out of equilibrium by two thermal baths with different temperatures connected to its ends, which control the current propagation. Transport is enhanced by applying a uniform radio-frequency pump field resonating with some of the spin-wave modes of the chain. Moreover, the two currents can be controlled independently by tuning the static field applied on the chain. Thus we describe two effective means for the independent control of coupled currents and the enhancement of thermal and spin-wave conductivity in a realistic magnonics device, suggesting that similar effects could be observed in a large class of nonlinear oscillating systems.

  • 27.
    Borlenghi, Simone
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Mahani, M. R.
    KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, Electrum 229, SE-16440 Kista, Sweden..
    Fangohr, Hans
    Univ Southampton, Dept Engn & Environm, Southampton SO17 1BJ, Hants, England.;European XFEL GmbH, Holzkoppel 4, D-22869 Schenefeld, Germany..
    Franchin, M.
    Univ Southampton, Dept Engn & Environm, Southampton SO17 1BJ, Hants, England..
    Delin, Anna
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, Electrum 229, SE-16440 Kista, Sweden.;KTH Royal Inst Technol, Swedish E Sci Res Ctr SeRC, SE-10044 Stockholm, Sweden..
    Fransson, Jonas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Micromagnetic simulations of spin-torque driven magnetization dynamics with spatially resolved spin transport and magnetization texture2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 9, artikkel-id 094428Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a simple and fast method to simulate spin-torque driven magnetization dynamics in nanopillar spin-valve structures. The approach is based on the coupling between a spin transport code based on random matrix theory and a micromagnetics finite-elements software. In this way the spatial dependence of both spin transport and magnetization dynamics is properly taken into account. Our results are compared with experiments. The excitation of the spin-wave modes, including the threshold current for steady-state magnetization precession and the nonlinear frequency shift of the modes are reproduced correctly. The giant magneto resistance effect and the magnetization switching also agree with experiment. The similarities with recently described spin-caloritronics devices are also discussed.

  • 28.
    Bouhon, Adrien
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Global band topology of simple and double Dirac-point semimetals2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 24, artikkel-id 241101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We combine space group representation theory together with the scanning of closed subdomains of the Brillouin zone with Wilson loops to algebraically determine the global band-structure topology. Considering space group No. 19 as a case study, we show that the energy ordering of the irreducible representations at the high-symmetry points {Gamma, S, T, U} fully determines the global band topology, with all topological classes characterized through their simple and double Dirac points.

  • 29.
    Bouhon, Adrien
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Slager, Robert-Jan
    Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany;Harvard Univ, Dept Phys, Cambridge, MA 02138 USA.
    Wilson loop approach to fragile topology of split elementary band representations and topological crystalline insulators with time-reversal symmetry2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 19, artikkel-id 195135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a general methodology toward the systematic characterization of crystalline topological insulating phases with time-reversal symmetry. In particular, taking the two-dimensional spinful hexagonal lattice as a proof of principle, we study windings of Wilson loop spectra over cuts in the Brillouin zone that are dictated by the underlying lattice symmetries. Our approach finds a prominent use in elucidating and quantifying the recently proposed "topological quantum chemistry" concept. Namely, we prove that the split of an elementary band representation (EBR) by a band gap must lead to a topological phase. For this we first show that in addition to the Fu-Kane-Mele Z(2) classification, there is C2T-symmetry-protected Z classification of two-band subspaces that is obstructed by the other crystalline symmetries, i.e., forbidding the trivial phase. This accounts for all nontrivial Wilson loop windings of split EBRs that are independent of the parametrization of the flow of Wilson loops. Then, by systematically embedding all combinatorial four-band phases into six-band phases, we find a refined topological feature of split EBRs. Namely, we show that while Wilson loop winding of split EBRs can unwind when embedded in higher-dimensional band space, two-band subspaces that remain separated by a band gap from the other bands conserve their Wilson loop winding, hence revealing that split EBRs are at least "stably trivial," i.e., necessarily nontrivial in the nonstable (few-band) limit but possibly trivial in the stable (many-band) limit. This clarifies the nature of fragile topology that has appeared very recently. We then argue that in the many-band limit, the stable Wilson loop winding is only determined by the Fu-Kane-Mele Z(2) invariant implying that further stable topological phases must belong to the class of higher-order topological insulators.

  • 30.
    Bouhon, Adrien
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Schmidt, Johann
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Topological nodal superconducting phases and topological phase transition in the hyperhoneycomb lattice2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 10, artikkel-id 104508Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We establish the topology of the spin-singlet superconducting states in the bare hyperhoneycomb lattice, and we derive analytically the full phase diagram using only symmetry and topology in combination with simple energy arguments. The phase diagram is dominated by two states preserving time-reversal symmetry. We find a line-nodal state dominating at low doping levels that is topologically nontrivial and exhibits surface Majorana flatbands, which we show perfectly match the bulk-boundary correspondence using the Berry phase approach. At higher doping levels, we find a fully gapped state with trivial topology. By analytically calculating the topological invariant of the nodal lines, we derive the critical point between the line-nodal and fully gapped states as a function of both pairing parameters and doping. We find that the line-nodal state is favored not only at lower doping levels but also if symmetry-allowed deformations of the lattice are present. Adding simple energy arguments, we establish that a fully gapped state with broken time-reversal symmetry likely appears covering the actual phase transition. We find this fully gapped state to be topologically trivial, while we find an additional point-nodal state at very low doing levels that also break time-reversal symmetry and has nontrivial topology with associated Fermi surface arcs. We eventually address the robustness of the phase diagram to generalized models also including adiabatic spin-orbit coupling, and we show how all but the point-nodal state are reasonably stable.

  • 31.
    Cayao, Jorge
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Odd-frequency superconducting pairing and subgap density of states at the edge of a two-dimensional topological insulator without magnetism2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 15, artikkel-id 155426Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the emergence and consequences of odd-frequency spin-triplet s-wave pairing in superconducting hybrid junctions at the edge of a two-dimensional topological insulator without any magnetism. More specifically, we consider several different normal-superconductor hybrid systems at the topological insulator edge, where spin-singlet s-wave superconducting pairing is proximity induced from an external conventional superconductor. We perform fully analytical calculations and show that odd-frequency mixed spin-triplet s-wave pairing arises due to the unique spin-momentum locking in the topological insulator edge state and the naturally nonconstant pairing potential profile in hybrid systems. Importantly, we establish a one-to-one correspondence between the local density of states (LDOS) at low energies and the odd-frequency spin-triplet pairing in NS, NSN, and SNS junctions along the topological insulator edge; at interfaces the enhancement in the LDOS can directly be attributed to the contribution of odd-frequency pairing. Furthermore, in SNS junctions we show that the emergence of the zero-energy LDOS peak at the superconducting phase phi = pi is associated purely with odd-frequency pairing in the middle of the junction.

  • 32.
    Cayao, Jorge
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Odd-frequency superconducting pairing in junctions with Rashba spin-orbit coupling2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 7, artikkel-id 075425Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider normal-superconductor (NS) and superconductor-normal-superconductor (SNS) junctions based on one-dimensional nanowires with Rashba spin-orbit coupling and proximity-induced s-wave spin-singlet superconductivity and analytically demonstrate how both even- and odd-frequency and spin-singlet and -triplet superconducting pair correlations are always present. In particular, by using a fully quantum mechanical scattering approach, we show that Andreev reflection induces mixing of spatial parities at interfaces, thus being the unique process which generates odd-frequency pairing; on the other hand, both Andreev and normal reflections contribute to even-frequency pairing. We further find that locally neither odd-frequency nor spin-triplet correlations are induced, but only even-frequency spin-singlet pairing. In the superconducting regions of NS junctions, the interface-induced amplitudes decay into the bulk, with the odd-frequency components being generally much larger than the even-frequency components at low frequencies. The odd-frequency pairing also develops short- and long-period oscillations due to the chemical potential and spin-orbit coupling, respectively, leading to a visible beating feature in their magnitudes. Moreover, we find that in short SNS junctions at pi-phase difference and strong spin-orbit coupling, the odd-frequency spin-singlet and -triplet correlations strongly dominate with an alternating spatial pattern for a large range of subgap frequencies.

  • 33.
    Cayao, Jorge
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    San-Jose, Pablo
    CSIC, ICMM, Cantoblanco, Madrid 28049, Spain..
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Aguado, Ramon
    CSIC, ICMM, Cantoblanco, Madrid 28049, Spain..
    Prada, Elsa
    Univ Autonoma Madrid, Dept Fis Mat Condensada, Condensed Matter Phys Ctr IFIMAC, E-28049 Madrid, Spain.;Univ Autonoma Madrid, Inst Nicolas Cabrera, E-28049 Madrid, Spain..
    Majorana splitting from critical currents in Josephson junctions2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 20, artikkel-id 205425Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A semiconducting nanowire with strong Rashba spin-orbit coupling and coupled to a superconductor can be tuned by an external Zeeman field into a topological phase with Majorana zero modes. Here we theoretically investigate how this exotic topological superconductor phase manifests in Josephson junctions based on such proximitized nanowires. In particular, we focus on critical currents in the short junction limit (L-N << xi, where L-N is the junction length and xi is the superconducting coherence length) and show that they contain important information about nontrivial topology and Majoranas. This includes signatures of the gap inversion at the topological transition and a unique oscillatory pattern that originates from Majorana interference. Interestingly, this pattern can be modified by tuning the transmission across the junction, thus providing complementary evidence of Majoranas and their energy splittings beyond standard tunnel spectroscopy experiments, while offering further tunability by virtue of the Josephson effect.

  • 34.
    Cedervall, Johan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Oorganisk kemi.
    Andersson, Martin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Mikrosystemteknik. Chalmers Univ Technol, Dept Chem & Chem Engn, SE-41296 Gothenburg, Sweden.
    Delczeg-Czirjak, Erna Krisztina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Iusan, Diana
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Pereiro, Manuel
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Roy, P.
    Radboud Univ Nijmegen, Inst Mol & Mat, Heyendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands.
    Ericsson, Tore
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Häggström, Lennart
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Lohstroh, W.
    Tech Univ Munich, Heinz Maier Leibnitz Zentrum MLZ, Garching Bei Munchen, Lichtenbergstr, D-185748 Garching, Germany.
    Mutka, H.
    Inst Laue Langevin, BP 156, F-38042 Grenoble 9, France.
    Sahlberg, Martin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Oorganisk kemi.
    Nordblad, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Deen, P. P.
    European Spallat Source ESS ERIC, Box 176, SE-22100 Lund, Sweden;Univ Copenhagen, Nanosci Ctr, Niels Bohr Inst, DK-2100 Copenhagen O, Denmark.
    Magnetocaloric effect in Fe2P: Magnetic and phonon degrees of freedom2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 17, artikkel-id 174437Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Devices based on magnetocaloric materials provide great hope for environmentally friendly and energy efficient cooling that does not rely on the use of harmful gasses. Fe2P based compounds are alloys that have shown great potential for magnetocaloric devices. The magnetic behavior in Fe2P is characterized by a strong magnetocaloric effect that coexists with a first-order magnetic transition (FOMT). Neutron diffraction and inelastic scattering, Mossbauer spectroscopy, and first-principles calculations have been used to determine the structural and magnetic state of Fe2P around the FOMT. The results reveal that ferromagnetic moments in the ordered phase are perturbed at the FOMT such that the moments cant away from the principle direction within a small temperature region. The acoustic-phonon modes reveal a temperature-dependent nonzero energy gap in the magnetically ordered phase that falls to zero at the FOMT. The interplay between the FOMT and the phonon energy gap indicates hybridization between magnetic modes strongly affected by spin-orbit coupling and phonon modes leading to magnon-phonon quasiparticles that drive the magnetocaloric effect.

  • 35.
    Chaurasiya, Avinash Kumar
    et al.
    SN Bose Natl Ctr Basic Sci, Dept Condensed Matter Phys & Mat Sci, Block JD,Sec 3, Kolkata 700106, India.
    Kumar, Akash
    Indian Inst Technol Delhi, Dept Phys, Thin Film Lab, New Delhi 110016, India.
    Gupta, Rahul
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Indian Inst Technol Delhi, Dept Phys, Thin Film Lab, New Delhi 110016, India.
    Chaudhary, Sujeet
    Indian Inst Technol Delhi, Dept Phys, Thin Film Lab, New Delhi 110016, India.
    Muduli, Pranaba Kishor
    Indian Inst Technol Delhi, Dept Phys, Thin Film Lab, New Delhi 110016, India.
    Barman, Anjan
    SN Bose Natl Ctr Basic Sci, Dept Condensed Matter Phys & Mat Sci, Block JD,Sec 3, Kolkata 700106, India.
    Direct observation of unusual interfacial Dzyaloshinskii-Moriya interaction in graphene/NiFe/Ta heterostructures2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 3, s. 1-6, artikkel-id 035402Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Graphene/ferromagnet interface promises a plethora of new science and technology. The interfacial Dzyaloshinskii-Moriya interaction (iDMI) is essential for stabilizing chiral spin textures, which are important for future spintronic devices. Here, we report direct observation of iDMI in graphene/Ni80Fe20/Ta heterostructures from nonreciprocity in spin-wave dispersion using Brillouin light-scattering technique. Linear scaling of iDMI with the inverse of Ni80Fe20 thicknesses suggests primarily interfacial origin of iDMI. Both iDMI and spinmixing conductance increase with the increase in defect density of graphene obtained by varying argon pressure during sputter deposition of Ni80Fe20. This suggests that the observed iDMI originates from defect-induced extrinsic spin-orbit coupling at the interface. The direct observation of iDMI at graphene/ferromagnet interface without perpendicular magnetic anisotropy opens a route in designing thin-film heterostructures based on two-dimensional materials for controlling chiral spin structure such as skyrmions and bubbles, and magnetic domain-wall-based storage and memory devices.

  • 36.
    Chernysheva, Ekaterina
    et al.
    UMR 125 CNRS St Gobain Rech, SVI, 39 Quai Lucien Lefranc, F-93303 Aubervilliers, France;Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Srour, Waked
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Philippe, Bertrand
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Baris, Bulent
    Sorbonne Univ, CNRS, Ecole Super Phys & Chim Ind, Lab Phys & Etud Mat,UMR 8213, 10 Rue Vauquelin, F-75005 Paris, France.
    Chenot, Stephane
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Felix Duarte, Roberto
    Helmholtz Zentrum Berlin Mat & Energie GmbH, D-12489 Berlin, Germany.
    Gorgoi, Mihaela
    Helmholtz Zentrum Berlin Mat & Energie GmbH, D-12489 Berlin, Germany.
    Cruguel, Herve
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Rensmo, Håkan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Montigaud, Herve
    UMR 125 CNRS St Gobain Rech, SVI, 39 Quai Lucien Lefranc, F-93303 Aubervilliers, France.
    Jupille, Jacques
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Cabailh, Gregory
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Grachev, Sergey
    UMR 125 CNRS St Gobain Rech, SVI, 39 Quai Lucien Lefranc, F-93303 Aubervilliers, France.
    Lazzari, Remi
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Band alignment at Ag/ZnO(0001) interfaces: A combined soft and hard x-ray photoemission study2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 23, artikkel-id 235430Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Band alignment at the interface between evaporated silver films and Zn- or O-terminated polar orientations of ZnO is explored by combining soft and hard x-ray photoemissions on native and hydrogenated surfaces. Ultraviolet photoemission spectroscopy (UPS) is used to track variations of work function, band bending, ionization energy, and Schottky barrier during silver deposition. The absolute values of band bending and the bulk position of the Fermi level are determined on continuous silver films by hard x-ray photoemission spectroscopy (HAXPES) through a dedicated modeling of core levels. Hydrogenation leads to the formation of similar to 0.3 monolayer of donorlike hydroxyl groups on both ZnO-O and ZnO-Zn surfaces and to the release of metallic zinc on ZnO-Zn. However, no transition to an accumulation layer is observed. On bare surfaces, silver adsorption is cationic on ZnO(000 (1) over bar)-O [anionic on ZnO(0001)-Zn] at the earliest stages of growth as expected from polarity healing before adsorbing as a neutral species. UPS and HAXPES data appear quite consistent. The two surfaces undergo rather similar band bendings for all types of preparation. The downward band bending of V-bb,(ZnO-O) = -0.4 eV and V-bb,(ZnO-Zn) = -0.6 eV found for the bare surfaces is reinforced upon hydrogenation (V-bb,(ZnO-O+H) = -1.1 eV, V-bb,(ZnO-Zn+H) = -1.2 eV). At the interface with Ag, a unique value of band bending of -0.75 eV is observed. While exposure to atomic hydrogen modulates strongly the energetic positions of the surface levels, a similar Schottky barrier of 0.5-0.7 eV is found for thick silver films on the two surfaces.

  • 37.
    Ciuciulkaite, Agne
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Östman, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Brucas, Rimantas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Kumar, Ankit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Verschuuren, Marc A.
    Philips Res Labs, High Tech Campus 4, Eindhoven, Netherlands.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Kapaklis, Vassilios
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Collective magnetization dynamics in nanoarrays of thin FePd disks2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 18, artikkel-id 184415Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the magnetization dynamics of a square array of mesoscopic disks, fabricated from an iron palladium alloy film. The dynamics properties were explored using ferromagnetic resonance measurements and micromagnetic simulations. The obtained spectra exhibit features resulting from the interactions between the disks, with a clear dependence on both temperature and the direction of the externally applied field. We demonstrate a qualitative agreement between the measured and calculated spectra. Furthermore, we calculated the mode profiles of the standing spin waves excited during time-dependent magnetic field excitations. The resulting maps confirm that the features appearing in the ferromagnetic resonance absorption spectra originate from the temperature- and directional-dependent interdisk interactions.

  • 38.
    Conradson, Steven D.
    et al.
    Inst Josef Stefan, Ljubljana 1000, Slovenia.;Washington State Univ, Pullman, WA 99164 USA..
    Andersson, David A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Boland, Kevin S.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Bradley, Joseph A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA.;Univ Washington, Seattle, WA 98195 USA..
    Byler, Darrin D.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Durakiewicz, Tomasz
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA.;Marie Curie Sklodowska Univ, PL-20031 Lublin, Poland..
    Gilbertson, Steven M.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Kozimor, Stosh A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Kvashnina, Kristina O.
    European Synchrotron ESRF, CS40220, F-38043 Grenoble 9, France.;Helmholtz Zentrum Dresden Rossendorf, Inst Resource Ecol, D-01314 Dresden, Germany..
    Nordlund, Dennis
    SLAC Natl Accelerator Lab, Menlo Pk, CA 94025 USA..
    Rodriguez, George
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Seidler, Gerald T.
    Univ Washington, Seattle, WA 98195 USA..
    Bagus, Paul S.
    Univ North Texas, Denton, TX 76203 USA..
    Butorin, Sergei
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Conradson, Dylan R.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Espinosa-Faller, Francisco J.
    Univ Marista Merida, Merida 97300, Yucatan, Mexico..
    Hess, Nancy J.
    Pacific Northwest Natl Lab, Richland, WA 99352 USA..
    Kas, Joshua J.
    Univ Washington, Seattle, WA 98195 USA..
    Lezama-Pacheco, Juan S.
    Stanford Univ, Stanford, CA 94305 USA..
    Martin, Philippe
    CEA, Nucl Energy Div, Res Dept Min & Fuel Recycling Proc, SFMA,LCC, F-30207 Bagnols Sur Ceze, France..
    Martucci, Mary B.
    Univ New Mexico, Los Alamos, NM 87544 USA..
    Rehr, John J.
    Univ Washington, Seattle, WA 98195 USA..
    Valdez, James A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Bishop, Alan R.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Baldinozzi, Gianguido
    Ecole Cent Paris, CNRS, F-99290 Chatenay Malabry, France..
    Clark, David L.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Tayal, Akhil
    Synchrotron Soleil, F-91192 Gif Sur Yvette, France..
    Closure of the Mott gap and formation of a superthermal metal in the Frohlich-type nonequilibrium polaron Bose-Einstein condensate in UO2+x2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 12, artikkel-id 125114Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mixed valence O-doped UO2+x. and photoexcited UO2 containing transitory U3+ and U5+ host a coherent polaronic quantum phase (CPQP) that exhibits the characteristics of a Frohlich-type, nonequilibrium, phononcoupled Bose-Einstein condensate whose stability and coherence are amplified by collective, anharmonic motions of atoms and charges. Complementary to the available, detailed, real space information from scattering and EXAFS, an outstanding question is the electronic structure. Mapping the Mott gap in UO2, U4O9, and U3O7 with O XAS and NIXS and UM5 RIXS shows that O doping raises the peak of the U5f states of the valence band by similar to 0.4 eV relative to a calculated value of 0.25 eV. However, it lowers the edge of the conduction band by 1.5 eV vs the calculated 0.6 eV, a difference much larger than the experimental error. This 1.9 eV reduction in the gap width constitutes most of the 2-2.2 eV gap measured by optical absorption. In addition, the XAS spectra show a tail that will intersect the occupied U5f states and give a continuous density-of-states that increases rapidly above its constricted intersection. Femtosecond-resolved photoemission measurements of UO2, coincident with the excitation pulse with 4.7 eV excitation, show the unoccupied U5f states of UO2 and no hot electrons. 3.1 eV excitation, however, complements the O-doping results by giving a continuous population of electrons for several eV above the Fermi level. The CPQP in photoexcited UO2 therefore fulfills the criteria for a nonequilibrium condensate. The electron distributions resulting from both excitations persist for 5-10 ps, indicating that they are the final state that therefore forms without passing through the initial continuous distribution of nonthermal electrons observed for other materials. Three exceptional findings are: (1) the direct formation of both of these long lived (> 3-10 ps) excited states without the short lived nonthermal intermediate; (2) the superthermal metallic state is as or more stable than typical photoinduced metallic phases; and (3) the absence of hot electrons accompanying the insulating UO2 excited state. This heterogeneous, nonequilibrium, Frohlich BEC stabilized by a Fano-Feshbach resonance therefore continues to exhibit unique properties.

  • 39.
    Cossu, Fabrizio
    et al.
    Asia Pacific Ctr Theoret Phys, Pohang 790784, Gyeongbuk, South Korea.
    Moghaddam, Ali G.
    IASBS, Dept Phys, Zanjan 4513766731, Iran.
    Kim, Kyoo
    POSTECH, Max Planck POSTECH Ctr Complex Phase Mat, Pohang 790784, South Korea.
    Tahini, Hassan A.
    Australian Natl Univ, Res Sch Phys & Engn, Dept Appl Math, Canberra, ACT 0200, Australia;UNSW Australia, Sch Chem Engn, IMDC, Sydney, NSW 2052, Australia.
    Di Marco, Igor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. Asia Pacific Ctr Theoret Phys, Pohang 790784, Gyeongbuk, South Korea; POSTECH, Dept Phys, Pohang 790784, Gyeongbuk, South Korea.
    Yeom, Han-Woong
    POSTECH, Dept Phys, Pohang 790784, Gyeongbuk, South Korea;Inst for Basic Sci Korea, Ctr forArtificial Low Dimens Elect Syst, Pohang 790784, South Korea.
    Akbari, Alireza
    Asia Pacific Ctr Theoret Phys, Pohang 790784, Gyeongbuk, South Korea;IASBS, Dept Phys, Zanjan 4513766731, Iran;POSTECH, Max Planck POSTECH Ctr Complex Phase Mat, Pohang 790784, South Korea;POSTECH, Dept Phys, Pohang 790784, Gyeongbuk, South Korea.
    Unveiling hidden charge density waves in single-layer NbSe2 by impurities2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 19, artikkel-id 195419Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We employ ab initio calculations to investigate the charge density waves in single-layer NbSe2, and we explore how they are affected by transition metal atoms. Our calculations reproduce the observed orthorhombic phase in single-layer NbSe2 in the clean limit, establishing the energy order between three different distorted structures, two consisting of triangular Nb-Nb clusters and a third, energetically unfavored, consisting of hexagonal Nb-Nb clusters. Such energy order, in agreement with known experimental work, is reversed by the adsorption of Co and Mn, which favor the formation of hexagonal Nb-Nb clusters; this CDW structure is indeed allowed from a symmetry point of view but hidden in pure single layers because it is at a higher energy. The other adsorbates, K and Ga, still favor one of the triangular Nb-Nb cluster, while suppressing the other. We report how the energy difference between such distorted structure varies with these adsorbates. Furthermore, transition metals induce magnetism and favor the reduction of the symmetry of the charge density distribution.

  • 40.
    Dankert, Andre
    et al.
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Bhaskar, Priyamvada
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Khokhriakov, Dmitrii
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Rodrigues, Isabel H.
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Karpiak, Bogdan
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Kamalakar, M. Venkata
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik. Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden.
    Charpentier, Sophie
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Garate, Ion
    Univ Sherbrooke, Inst Quant & Regrp Quebecois Mat Pointe, Dept Phys, Sherbrooke, PQ J1K 2R1, Canada..
    Dash, Saroj P.
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Origin and evolution of surface spin current in topological insulators2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 12, artikkel-id 125414Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Dirac surface states of topological insulators offer a unique possibility for creating spin polarized charge currents due to the spin-momentum locking. Here we demonstrate that the control over the bulk and surface contribution is crucial to maximize the charge-to-spin conversion efficiency. We observe an enhancement of the spin signal due to surface-dominated spin polarization while freezing out the bulk conductivity in semiconducting Bi1.5Sb0.5Te1.7Se1.3 below 100 K. Detailed measurements up to room temperature exhibit a strong reduction of the magnetoresistance signal between 2 and 100 K, which we attribute to the thermal excitation of bulk carriers and to the electron-phonon coupling in the surface states. The presence and dominance of this effect up to room temperature is promising for spintronic science and technology.

  • 41.
    Di Marco, Igor
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Held, Andreas
    Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Keshavarz, Samara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Kvashnin, Yaroslav O
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Chioncel, Liviu
    Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany..
    Half-metallicity and magnetism in the Co2MnAl/CoMnVAl heterostructure2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 3, artikkel-id 035105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a study of the electronic structure and magnetism of Co2MnAl, CoMnVAl, and their heterostructure. We employ a combination of density-functional theory and dynamical mean-field theory (DFT+DMFT). We find that Co2MnAl is a half-metallic ferromagnet, whose electronic and magnetic properties are not drastically changed by strong electronic correlations, static or dynamic. Nonquasiparticle states are shown to appear in the minority spin gap without affecting the spin polarization at the Fermi level predicted by standard DFT. We find that CoMnVAl is a semiconductor or a semimetal, depending on the employed computational approach. We then focus on the electronic and magnetic properties of the Co2MnAl/CoMnVAl heterostructure, predicted by previous first-principle calculations as a possible candidate for spin-injecting devices. We find that two interfaces, Co-Co/V-Al and Co-Mn/Mn-Al, preserve the half-metallic character, with and without including electronic correlations. We also analyze the magnetic exchange interactions in the bulk and at the interfaces. At the Co-Mn/Mn-Al interface, competing magnetic interactions are likely to favor the formation of a noncollinear magnetic order, which is detrimental for the spin polarization.

  • 42.
    Dong, Zhihua
    et al.
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Li, Wei
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Chen, Dengfu
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Schonecker, Stephan
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Long, Mujun
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Vitos, Levente
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Longitudinal spin fluctuation contribution to thermal lattice expansion of paramagnetic Fe2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 5, artikkel-id 054426Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using an efficient first-principles computational scheme for paramagnetic body-centered cubic (bcc) and face-centered cubic (fcc) Fe, we investigate the impact of thermal longitudinal spin fluctuations (LSFs) on the thermal lattice expansion. The equilibrium physical parameters are derived from the self-consistent Helmholtz free energy, in which the LSFs are considered within the adiabatic approximation and the anharmonic lattice vibration effect is included using the Debye-Gruneisen model taking into account the interplay between thermal, magnetic, and elastic degrees of freedom. Thermal LSFs are energetically more favorable in the fcc phase than in the bcc one giving a sizable contribution to the linear thermal expansion of gamma-Fe. The present scheme leads to accurate temperature-dependent equilibriumWigner-Seitz radius, bulk modulus, and Debye temperature within the stability fields of the two phases and demonstrates the importance of thermal spin fluctuations in paramagnetic Fe.

  • 43.
    Dong, Zhihua
    et al.
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Schonecker, Stephan
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Chen, Dengfu
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Li, Wei
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Long, Mujun
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Vitos, Levente
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Elastic properties of paramagnetic austenitic steel at finite temperature: Longitudinal spin fluctuations in multicomponent alloys2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 17, artikkel-id 174415Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a first-principles framework for longitudinal spin fluctuations (LSFs) in disordered paramagnetic (PM) multicomponent alloy systems and apply it to investigate the influence of LSFs on the temperature dependence of two elastic constants of PM austenitic stainless steel Fe15Cr15Ni. The magnetic model considers individual fluctuating moments in a static PM medium with first-principles-derived LSF energetics in conjunction with describing chemical disorder and randomness of the transverse magnetic component in the single-site alloy formalism and disordered local moment (DLM) picture. A temperature-sensitive mean magnetic moment is adopted to accurately represent the LSF state in the elastic-constant calculations. We make evident that magnetic interactions between an LSF impurity and the PM medium are weak in the present steel alloy. This allows gaining accurate LSF energetics and mean magnetic moments already through a perturbation from the static DLM moments instead of a tedious self-consistent procedure. We find that LSFs systematically lower the cubic shear elastic constants c' and c(44) by similar to 6 GPa in the temperature interval 300-1600 K, whereas the predominant mechanism for the softening of both elastic constants with temperature is the magneto-volume coupling due to thermal lattice expansion. We find that non-negligible local magnetic moments of Cr and Ni are thermally induced by LSFs, but they exert only a small influence on the elastic properties. The proposed framework exhibits high flexibility in accurately accounting for finite-temperature magnetism and its impact on the mechanical properties of PM multicomponent alloys.

  • 44.
    Du, Dou
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Wolf, Matthew J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Hermansson, Kersti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Broqvist, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
    Screened hybrid functionals applied to ceria: Effect of Fock exchange2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 23, artikkel-id 235203Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate how the redox properties of ceria are affected by the fraction of Fock exchange in screened HSE06-based hybrid density functionals, and we compare with PBE+U results, and with experiments when available. We find that using similar to 15% Fock exchange yields a good compromise with respect to structure, electronic structure, and calculated reduction energies, and represents a significant improvement over the PBE+U results. We also investigate the possibility to use a computationally cheaper HSE06//PBE+U protocol consisting of structure optimization with PBE+U, a subsequent lattice parameter rescaling step, and, finally, a single-point full hybrid calculation. We find that such a composite computational protocol works very well and yields results in close agreement with those where HSE06 was used also for the structure optimization.

  • 45.
    Duan, Yu-Xia
    et al.
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China.
    Zhang, Cheng
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China.
    Rusz, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Oppeneer, Peter M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Durakiewicz, Tomasz
    Marie Curie Sklodowska Univ, Lnstitute Phys, PL-20031 Lublin, Poland.
    Sassa, Yasmine
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Tjernberg, Oscar
    KTH Royal Inst Technol, Dept Appl Phys, Electrum 229, SE-16440 Stockholm, Kista, Sweden.
    Mansson, Martin
    KTH Royal Inst Technol, Dept Appl Phys, Electrum 229, SE-16440 Stockholm, Kista, Sweden.
    Berntsen, Magnus H.
    KTH Royal Inst Technol, Dept Appl Phys, Electrum 229, SE-16440 Stockholm, Kista, Sweden.
    Wu, Fan-Ying
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China.
    Zhao, Yin-Zou
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China.
    Song, Jiao-Jiao
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China.
    Wu, Qi-Yi
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China.
    Luo, Yang
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China.
    Bauer, Eric D.
    Los Alamos Natl Lab, Condensed Matter & Magnet Sci Grp, Los Alamos, NM 87545 USA.
    Thompson, Joe D.
    Los Alamos Natl Lab, Condensed Matter & Magnet Sci Grp, Los Alamos, NM 87545 USA.
    Meng, Jian-Qiao
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China;Hunan Normal Univ, SICQEA, Changsha 410081, Hunan, Peoples R China.
    Crystal electric field splitting and f-electron hybridization in heavy-fermion CePt2In72019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 8, artikkel-id 085141Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use high-resolution angle-resolved photoemission spectroscopy to investigate the electronic structure of the antiferromagnetic heavy fermion compound CePt2In7, which is amember of the CeIn3-derived heavy fermion material family. Weak hybridization among 4f electron states and conduction bands was identified in CePt2In7 at low temperature much weaker than that in the other heavy fermion compounds like CeIrIn5 and CeRhIn5. The Ce 4f spectrum shows fine structures near the Fermi energy, reflecting the crystal electric field splitting of the 4f(5/2)(1) and 4f(7/2)(1) states. Also, we find that the Fermi surface has a strongly three-dimensional topology, in agreement with density-functional theory calculations.

  • 46.
    Dutta, Paramita
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Black-Schaffer, Annica M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Signature of odd-frequency equal-spin triplet pairing in the Josephson current on the surface of Weyl nodal loop semimetals2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 10, artikkel-id 104511Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We theoretically predict proximity-induced odd-frequency (odd-omega) pairing on the surface of a Weyl nodal loop semimetal, characterized by a nodal loop Fermi surface and drumheadlike surface states (DSSs), attached to conventional spin-singlet s-wave superconducting leads. Due to the complete spin polarization of the DSS, only odd-omega equal-spin triplet pairing is present, and we show that it gives rise to a finite Josephson current. Placing an additional ferromagnet in the junction can also generate odd-omega) mixed-spin triplet pairing, but the pairing and current are not affected if the magnetization is orthogonal to the DSS spin polarization, which further confirms the equal-spin structure of the pairing.

  • 47.
    Edstrom, Alexander
    et al.
    Swiss Fed Inst Technol, Mat Theory, Wolfgang Pauli Str 27, CH-8093 Zurich, Switzerland.
    Lubk, Axel
    IFW Dresden, Inst Solid State Res, Helmholtzstr 20, D-01069 Dresden, Germany;Tech Univ Dresden, Inst Solid State & Mat Phys, Haeckelstr 3, D-01069 Dresden, Germany.
    Rusz, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Quantum mechanical treatment of atomic-resolution differential phase contrast imaging of magnetic materials2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 17, artikkel-id 174428Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Utilizing the Pauli equation based multislice method, introduced in a previous paper [A. Edstrom, A. Lubk, and J. Rusz, Phys. Rev. Lett. 116, 127203 (2016)], we study the atomic-resolution differential phase contrast (DPC) imaging on an example of a hard magnet FePt with in-plane magnetization. Simulated center-of-mass pattern in a scanning transmission electron microscopy experiment carries information about both electric and magnetic fields. The momentum transfer remains curl free, which has consequences for interpretation of the integrated DPC technique. The extracted magnetic component of the pattern is compared to the expected projected microscopic magnetic field as obtained by density functional theory calculation. Qualitative agreement is obtained for low sample thicknesses and a suitable range of collection angles.

  • 48.
    Edström, Alexander
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori. ETH, Mat Theory, Wolfgang Pauli Str 27, CH-8093 Zurich, Switzerland..
    Magnetocrystalline anisotropy of Laves phase Fe2Ta1-xWx from first principles: Effect of 3d-5d hybridization2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 6, artikkel-id 064422Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    ThemaThe magnetic properties of Fe2Ta and Fe2W in the hexagonal Laves phase are computed using density functional theory in the generalized gradient approximation, with the full potential linearized augmented plane-wave method. The alloy Fe2Ta1−xWx is studied using the virtual crystal approximation to treat disorder, with some comparisons to supercell calculations. Fe2Ta is found to be ferromagnetic with a saturation magnetization of μ0Ms=0.66T while, in contrast to earlier computational work, Fe2W is found to be ferrimagnetic with μ0Ms=0.35T. The transition from the ferri- to the ferromagnetic state occurs for x≤0.1. The magnetocrystalline anisotropy energy (MAE) is calculated to 1.25MJ/m3 for Fe2Ta and 0.87MJ/m3 for Fe2W. The MAE is found to be smaller for all values x in Fe2Ta1−xWx than for the end compounds and it is negative (in-plane anisotropy) for 0.1≤x≤0.9. The MAE is carefully analyzed in terms of the electronic structure. Even though there are weak 5d contributions to the density of states at the Fermi energy in both end compounds, a reciprocal space analysis, using the magnetic force theorem, reveals that the MAE originates mainly from regions of the Brillouin zone with strong 3d−5d hybridization near the Fermi energy. Perturbation theory and its applicability in relation to the MAE is discussed.

  • 49.
    Ertan, Emelie
    et al.
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, S-10691 Stockholm, Sweden..
    Kimberg, Victor
    Royal Inst Technol, Theoret Chem & Biol, S-10691 Stockholm, Sweden.;Siberian Fed Univ, Inst Nanotechnol Spect & Quantum Chem, Krasnoyarsk 660041, Russia..
    Gel'mukhanov, Faris
    Royal Inst Technol, Theoret Chem & Biol, S-10691 Stockholm, Sweden.;Siberian Fed Univ, Inst Nanotechnol Spect & Quantum Chem, Krasnoyarsk 660041, Russia..
    Hennies, Franz
    Lund Univ, MAX Lab 4, S-22100 Lund, Sweden..
    Rubensson, Jan-Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Schmitt, Thorsten
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Strocov, Vladimir N.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Zhou, Kejin
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland.;Diamond Light Source Ltd, Diamond House,Harwell Sci & Innovat Campus, Didcot OX11 0DE, Oxon, England..
    Iannuzzi, Marcella
    Univ Zurich, Inst Phys Chem, CH-8057 Zurich, Switzerland..
    Foehlisch, Alexander
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Odelius, Michael
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, S-10691 Stockholm, Sweden..
    Pietzsch, Annette
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Theoretical simulations of oxygen K-edge resonant inelastic x-ray scattering of kaolinite2017Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 14, artikkel-id 144301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Near-edge x-ray absorption fine structure (NEXAFS) and resonant inelastic x-ray scattering (RIXS) measurements at the oxygen K edge were combined with theoretical spectrum simulations, based on periodic density functional theory and nuclear quantum dynamics, to investigate the electronic structure and chemical bonding in kaolinite Al2Si2O5(OH)(4). We simulated NEXAFS spectra of all crystallographically inequivalent oxygen atoms in the crystal and RIXS spectra of the hydroxyl groups. Detailed insight into the ground-state potential energy surface of the electronic states involved in the RIXS process were accessed by analyzing the vibrational excitations, induced by the core excitation, in quasielastic scattering back to the electronic ground state. In particular, we find that the NEXAFS pre-edge is dominated by features related to OH groups within the silica and alumina sheets, and that the vibrational progression in RIXS can be used to selectively probe vibrational modes of this subclass of OH groups. The signal is dominated by the OH stretching mode, but also other lower vibrational degrees of freedom, mainly hindered rotational modes, contribute to the RIXS signal.

  • 50.
    Etter, Sarah B.
    et al.
    Swiss Fed Inst Technol, Inst Theoret Phys, CH-8093 Zurich, Switzerland..
    Bouhon, Adrien
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Sigrist, Manfred
    Swiss Fed Inst Technol, Inst Theoret Phys, CH-8093 Zurich, Switzerland..
    Spontaneous surface flux pattern in chiral p-wave superconductors2018Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 6, artikkel-id 064510Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In chiral p-wave superconductors, magnetic flux patterns may appear spontaneously when translational symmetry is broken such as at surfaces, domain walls, or impurities. However, in the candidate material Sr2RuO4 no direct signs of such magnetic fields have been detected experimentally. In this paper, the flux pattern at the edge of a disk-shaped sample is examined using the phenomenological Ginzburg-Landau approach. The detailed shape of the flux pattern, including self-screening, is computed numerically for different surface types by systematically scanning a range of boundary conditions. Moreover, specific features of the electronic structure are included qualitatively through the coefficients in the Ginzburg-Landau functional. Both the shape and the magnitude of the flux pattern are found to be highly sensitive to all considered parameters. In conclusion, such spontaneous magnetic flux patterns are not a universal feature of chiral p-wave superconductors.

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