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Mydosh, J. A., Oppeneer, P. M. & Riseborough, P. S. (2020). Hidden order and beyond: an experimental-theoretical overview of the multifaceted behavior of URu2Si2. Journal of Physics: Condensed Matter, 32(14), Article ID 143002.
Open this publication in new window or tab >>Hidden order and beyond: an experimental-theoretical overview of the multifaceted behavior of URu2Si2
2020 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 32, no 14, article id 143002Article, review/survey (Refereed) Published
Abstract [en]

This topical review describes the multitude of unconventional behaviors in the hidden order, heavy fermion, antiferromagnetic and superconducting phases of the intermetallic compound URu2Si2 when tuned with pressure, magnetic field, and substitutions for all three elements. Such 'perturbations' result in a variety of new phases beyond the mysterious hidden order that are only now being slowly understood through a series of state-of-the-science experimentation, along with an array of novel theoretical approaches. Despite all these efforts spanning more than 30 years, hidden order (HO) remains puzzling and non-clarified, and the search continues in 2019 into a fourth decade for its final resolution. Here we attempt to update the present situation of URu2Si2 importing the latest experimental results and theoretical proposals. First, let us consider the pristine compound as a function of temperature and report the recent measurements and models relating to its heavy Fermi liquid crossover, its HO and superconductivity (SC). Recent experiments and theories are surmized that address four-fold symmetry breaking (or nematicity), Isingness and unconventional excitation modes. Second, we review the pressure dependence of URu2Si2 and its transformation to antiferromagnetic long-range order. Next we confront the dramatic high magnetic-field phases requiring fields above 40 T. And finally, we attempt to answer how does random substitutions of other 5f elements for U, and 3d, 4d, and 5d elements for Ru, and even P for Si affect and transform the HO. Commensurately, recent theoretical models are summarized and then related to the intriguing experimental behavior.

Keywords
hidden order, unconventional superconductivity, correlated electron system, Isingness, multifaceted phases
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-407486 (URN)10.1088/1361-648X/ab5eba (DOI)000514841500001 ()31801118 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060Swedish National Infrastructure for Computing (SNIC)
Available from: 2020-03-25 Created: 2020-03-25 Last updated: 2020-03-25Bibliographically approved
Duan, Y.-X., Zhang, C., Rusz, J., Oppeneer, P. M., Durakiewicz, T., Sassa, Y., . . . Meng, J.-Q. (2019). Crystal electric field splitting and f-electron hybridization in heavy-fermion CePt2In7. Physical Review B, 100(8), Article ID 085141.
Open this publication in new window or tab >>Crystal electric field splitting and f-electron hybridization in heavy-fermion CePt2In7
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 8, article id 085141Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-398850 (URN)10.1103/PhysRevB.100.085141 (DOI)000482582200008 ()
Funder
Swedish Research Council, 2017-05078Swedish Research Council, INCA-2014-6426Knut and Alice Wallenberg FoundationSwedish Research Council, 2016-06955Swedish Research CouncilCarl Tryggers foundation , CTS-16: 324Carl Tryggers foundation , CTS-17:325
Available from: 2019-12-18 Created: 2019-12-18 Last updated: 2019-12-18Bibliographically approved
Bekaert, J., Petrov, M., Aperis, A., Oppeneer, P. M. & Milosevic, M. V. (2019). Hydrogen-Induced High-Temperature Superconductivity in Two-Dimensional Materials: The Example of Hydrogenated Monolayer MgB2. Physical Review Letters, 123(7), Article ID 077001.
Open this publication in new window or tab >>Hydrogen-Induced High-Temperature Superconductivity in Two-Dimensional Materials: The Example of Hydrogenated Monolayer MgB2
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2019 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 7, article id 077001Article in journal (Refereed) Published
Abstract [en]

Hydrogen-based compounds under ultrahigh pressure, such as the polyhydrides H3S and LaH10, superconduct through the conventional electron-phonon coupling mechanism to attain the record critical temperatures known to date. Here we exploit the intrinsic advantages of hydrogen to strongly enhance phonon-mediated superconductivity in a completely different system, namely, a two-dimensional material with hydrogen adatoms. We find that van Hove singularities in the electronic structure, originating from atomiclike hydrogen states, lead to a strong increase of the electronic density of states at the Fermi level, and thus of the electron-phonon coupling. Additionally, the emergence of high-frequency hydrogen-related phonon modes in this system boosts the electron-phonon coupling further. As a concrete example, we demonstrate the effect of hydrogen adatoms on the superconducting properties of monolayer MgB2, by solving the fully anisotropic Eliashberg equations, in conjunction with a first-principles description of the electronic and vibrational states, and their coupling. We show that hydrogenation leads to a high critical temperature of 67 K, which can be boosted to over 100 K by biaxial tensile strain.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-393662 (URN)10.1103/PhysRevLett.123.077001 (DOI)000480611900017 ()
Funder
Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC)
Available from: 2019-09-25 Created: 2019-09-25 Last updated: 2019-09-25Bibliographically approved
Schrodi, F., Aperis, A. & Oppeneer, P. M. (2019). Increased performance of Matsubara space calculations: A case study within Eliashberg theory. Physical Review B, 99(18), Article ID 184508.
Open this publication in new window or tab >>Increased performance of Matsubara space calculations: A case study within Eliashberg theory
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 18, article id 184508Article in journal (Refereed) Published
Abstract [en]

We present a method to considerably improve the numerical performance for solving Eliashberg-type coupled equations on the imaginary axis. Instead of the standard practice of introducing a hard numerical cutoff for treating the infinite summations involved, our scheme allows for the efficient calculation of such sums extended formally up to infinity. The method is first benchmarked with isotropic Migdal-Eliashberg theory calculations and subsequently applied to the solution of the full-bandwidth, multiband, and anisotropic equations focusing on the FeSe/SrTiO3 interface as a case study. Compared to the standard procedure, we reach similarly well converged results with less than one fifth of the number of frequencies for the anisotropic case, while for the isotropic set of equations we spare approximately ninety percent of the complexity. Since our proposed approximations are very general, our numerical scheme opens the possibility of studying the superconducting properties of a wide range of materials at ultralow temperatures.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-387593 (URN)10.1103/PhysRevB.99.184508 (DOI)000469055500010 ()
Funder
Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC)
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-06-26Bibliographically approved
Reddy, I. R., Oppeneer, P. M. & Tarafder, K. (2019). Interfacial Spin Manipulation of Nickel-Quinonoid Complex Adsorbed on Co(001) Substrate. MAGNETOCHEMISTRY, 5(1), Article ID 2.
Open this publication in new window or tab >>Interfacial Spin Manipulation of Nickel-Quinonoid Complex Adsorbed on Co(001) Substrate
2019 (English)In: MAGNETOCHEMISTRY, ISSN 2312-7481, Vol. 5, no 1, article id 2Article in journal (Refereed) Published
Abstract [en]

We studied the structural, electronic, and magnetic properties of a recently synthesized Ni(II)-quinonoid complex upon adsorption on a magnetic Co(001) substrate. Our density functional theory +U (DFT+U) calculations predict that the molecule undergoes a spin-state switching from low-spin S = 0 in the gas phase to high-spin S approximate to 1 when adsorbed on the Co(001) surface. A strong covalent interaction of the quinonoid rings and surface atoms leads to an increase of the Ni-O(N) bond lengths in the chemisorbed molecule that support the spin-state switching. Our DFT+U calculations show that the molecule is ferromagnetically coupled to the substrate. The Co surface-Ni center exchange mechanism was carefully investigated. We identified an indirect exchange interaction via the quinonoid ligands that stabilizes the molecule's spin moment in ferromagnetic alignment with the Co surface magnetization.

Keywords
spin-state switching, interfacial spin-manipulation, DFT+U theory
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-392066 (URN)10.3390/magnetochemistry5010002 (DOI)000477013300002 ()
Funder
Swedish Research Council, SB/FTP/PS-032/2014Knut and Alice Wallenberg Foundation, 2015.0060
Available from: 2019-09-09 Created: 2019-09-09 Last updated: 2019-09-09Bibliographically approved
Alekhin, A., Razdolski, I., Berritta, M., Buerstel, D., Temnov, V., Diesing, D., . . . Melnikov, A. (2019). Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces. Journal of Physics: Condensed Matter, 31(12), Article ID 124002.
Open this publication in new window or tab >>Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces
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2019 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 12, article id 124002Article in journal (Refereed) Published
Abstract [en]

We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy- and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm fs(-1) (close to the Fermi velocity) and the decay length on the order of 100nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
spin current, time-resolved MOKE, nonlinear magneto-optical spectroscopy, Drude model
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-377198 (URN)10.1088/1361-648X/aafd06 (DOI)000457442600001 ()30625433 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060EU, Horizon 2020, 737709
Available from: 2019-02-25 Created: 2019-02-25 Last updated: 2019-02-25Bibliographically approved
Arruda, L. M., Ali, M. E. E., Bernien, M., Nickel, F., Kopprasch, J., Czekelius, C., . . . Kuch, W. (2019). Modifying the Magnetic Anisotropy of an Iron Porphyrin Molecule by an on-Surface Ring-Closure Reaction. The Journal of Physical Chemistry C, 123(23), 14547-14555
Open this publication in new window or tab >>Modifying the Magnetic Anisotropy of an Iron Porphyrin Molecule by an on-Surface Ring-Closure Reaction
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2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 23, p. 14547-14555Article in journal (Refereed) Published
Abstract [en]

The magnetic properties of adsorbed metalloporphyrin molecules can be altered or tuned by the substrate, additional axial ligands, or changes to the molecules' macrocycle. These modifications influence the electronic configuration of the fourfold-coordinated central metal ion that is responsible for the metalloporphyrins' magnetic properties. We report a substantial increase in the effective spin moment obtained from sum-rule analysis of X-ray magnetic circular dichroism for an iron metalloporphyrin molecule on Au(111) through its conversion from iron(II)-octaethylporphyrin to iron(II)-tetrabenzoporphyrin in a surface-assisted ring-closure ligand reaction. Density functional theory calculations with additional strong Coulomb correlation (DFT+U) show that the on-surface reaction alters the conformation of the molecule, increasing its planarity and the ion-surface distance. A spin-Hamiltonian fit of the magnetization as a function of field reveals a substantial increase in the intra-atomic magnetic dipole term (T-z) and a decrease in the magnitude of the easy-plane anisotropy upon ring closure. This consequence of the ring closure demonstrates how new magnetic properties can be obtained from on-surface reactions, resulting here in significant modifications to the magnetic anisotropy of the Fe ion, and sheds light onto the molecule-substrate interaction in these systems.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-390210 (URN)10.1021/acs.jpcc.9b03126 (DOI)000471834000049 ()
Funder
Swedish Research CouncilGerman Research Foundation (DFG), SFB 658
Available from: 2019-08-09 Created: 2019-08-09 Last updated: 2019-08-09Bibliographically approved
Salemi, L., Berritta, M., Nandy, A. K. & Oppeneer, P. M. (2019). Orbitally dominated Rashba-Edelstein effect in noncentrosymmetric antiferromagnets. Nature Communications, 10, Article ID 5381.
Open this publication in new window or tab >>Orbitally dominated Rashba-Edelstein effect in noncentrosymmetric antiferromagnets
2019 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 5381Article in journal (Refereed) Published
Abstract [en]

Efficient manipulation of magnetic order with electric current pulses is desirable for achieving fast spintronic devices. The Rashba-Edelstein effect, wherein spin polarization is electrically induced in noncentrosymmetric systems, provides a mean to achieve staggered spin-orbit torques. Initially predicted for spin, its orbital counterpart has been disregarded up to now. Here we report a generalized Rashba-Edelstein effect, which generates not only spin polarization but also orbital polarization, which we find to be far from being negligible. We show that the orbital Rashba-Edelstein effect does not require spin-orbit coupling to exist. We present first-principles calculations of the frequency-dependent spin and orbital Rashba-Edelstein tensors for the noncentrosymmetric antiferromagnets CuMnAs and Mn2Au. We show that the electrically induced local magnetization can exhibit Rashba-like or Dresselhaus-like symmetries, depending on the magnetic configuration. We compute sizable induced magnetizations at optical frequencies, which suggest that electric-field driven switching could be achieved at much higher frequencies.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-398428 (URN)10.1038/s41467-019-13367-z (DOI)000498702100001 ()31772174 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060Swedish National Infrastructure for Computing (SNIC)EU, Horizon 2020, 737709
Available from: 2019-12-06 Created: 2019-12-06 Last updated: 2019-12-06Bibliographically approved
Mondal, R., Donges, A., Ritzmann, U., Oppeneer, P. M. & Nowak, U. (2019). Terahertz spin dynamics driven by a field-derivative torque. Physical Review B, 100(6), Article ID 060409.
Open this publication in new window or tab >>Terahertz spin dynamics driven by a field-derivative torque
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 6, article id 060409Article in journal (Refereed) Published
Abstract [en]

Efficient manipulation of magnetization at ultrashort timescales is of particular interest for future technology. Here, we numerically investigate the influence of the so-called field-derivative torque, which was derived earlier based on relativistic Dirac theory [R. Mondal et al., Phys. Rev. B 94, 144419 (2016)], on the spin dynamics triggered by ultrashort laser pulses. We find that only considering the THz Zeeman field can underestimate the spin excitation in antiferromagnetic oxide systems such as, e.g., NiO and CoO. However, accounting for both the THz Zeeman torque and the field-derivative torque, the amplitude of the spin excitation increases significantly. Studying the damping dependence of the field-derivative torque we observe larger effects for materials having larger damping constants.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-398853 (URN)10.1103/PhysRevB.100.060409 (DOI)000482447200001 ()
Funder
Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC)Knut and Alice Wallenberg Foundation, 2015.0060
Available from: 2019-12-11 Created: 2019-12-11 Last updated: 2019-12-11Bibliographically approved
Yamamoto, K., Kubota, Y., Suzuki, M., Hirata, Y., Carva, K., Berritta, M., . . . Wadati, H. (2019). Ultrafast demagnetization of Pt magnetic moment in L1(0)-FePt probed by magnetic circular dichroism at a hard x-ray free electron laser. New Journal of Physics, 21(12), Article ID 123010.
Open this publication in new window or tab >>Ultrafast demagnetization of Pt magnetic moment in L1(0)-FePt probed by magnetic circular dichroism at a hard x-ray free electron laser
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2019 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 21, no 12, article id 123010Article in journal (Refereed) Published
Abstract [en]

Unraveling the origin of ultrafast demagnetization in multisublattice ferromagnetic materials requires femtosecond x-ray techniques to trace the magnetic moment dynamics on individual elements, but this could not yet be achieved in the hard x-ray regime. We demonstrate here the first ultrafast demagnetization dynamics in the ferromagnetic heavy 5d-transition metal Pt using circularly-polarized hard x-rays at an x-ray free electron laser (XFEL). The decay time of laser-induced demagnetization of L1(0)-FePt is determined to be tau(Pt) = 0.61 +/- 0.04 ps using time-resolved x-ray magnetic circular dichroism at the Pt L-3 edge, whereas magneto-optical Kerr measurements indicate the decay time for the total magnetization as tau(total) < 0.1 ps. A transient magnetic state with a photomodulated ratio of the 3d and 5d magnetic moments is demonstrated for pump-probe delays larger than 1 ps. We explain this distinct photo-modulated transient magnetic state by the induced-moment behavior of the Pt atom and the x-ray probing depth. Our findings pave the way for the future use of XFELs to disentangle atomic spin dynamics contributions.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
photo-induced magnetization dynamics, time-resolved XMCD, XFEL
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-407454 (URN)10.1088/1367-2630/ab5ac2 (DOI)000513663400009 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060
Available from: 2020-03-26 Created: 2020-03-26 Last updated: 2020-03-26Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-9069-2631

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