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Maldonado, Pablo
Publications (10 of 35) Show all publications
Maldonado, P. & Kvashnin, Y. (2019). Microscopic theory of ultrafast out-of-equilibrium magnon-phonon dynamics in insulators. Physical Review B, 100(1), Article ID 014430.
Open this publication in new window or tab >>Microscopic theory of ultrafast out-of-equilibrium magnon-phonon dynamics in insulators
2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 1, article id 014430Article in journal (Refereed) Published
Abstract [en]

The interaction between lattice and spins is at the heart of an extremely intriguing ultrafast dynamics in magnetic materials. In this paper, we formulate a general nonequilibrium theory that disentangles the complex interplay between phonons and magnons in a THz laser-excited antiferromagnetic insulator. The theory provides a quantitative description of the transient energy flow between the spin and lattice subsystems, subject to magnon-phonon and phonon-phonon scatterings, giving rise to finite lifetimes of the quasiparticles and to the equilibration time of the system. We predict a kind of scattering process where two magnons of opposite polarizations decay into a phonon, previously omitted in the literature. The theory is combined with first-principles calculations and then applied to simulate realistic dynamics of NiO. The main relaxation channels and hot spots in the reciprocal space, giving the strongest contribution to the energy transfer between phonons and magnons are identified. The diverse interaction strengths lead to distinct coupled dynamics of the lattice and spin systems and subsequently to different equilibration timescales.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-392582 (URN)10.1103/PhysRevB.100.014430 (DOI)000477883500003 ()
Funder
Swedish Research Council, 2016-03875Swedish National Infrastructure for Computing (SNIC)
Available from: 2019-09-09 Created: 2019-09-09 Last updated: 2019-09-09Bibliographically approved
Reid, A. H., Shen, X., Maldonado, P., Chase, T., Jal, E., Granitzka, P. W., . . . Dürr, H. A. (2018). Beyond a phenomenological description of magnetostriction. Nature Communications, 9, Article ID 388.
Open this publication in new window or tab >>Beyond a phenomenological description of magnetostriction
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2018 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 388Article in journal (Refereed) Published
Abstract [en]

Magnetostriction, the strain induced by a change in magnetization, is a universal effect in magnetic materials. Owing to the difficulty in unraveling its microscopic origin, it has been largely treated phenomenologically. Here, we show how the source of magnetostriction-the underlying magnetoelastic stress-can be separated in the time domain, opening the door for an atomistic understanding. X-ray and electron diffraction are used to separate the subpicosecond spin and lattice responses of FePt nanoparticles. Following excitation with a 50-fs laser pulse, time-resolved X-ray diffraction demonstrates that magnetic order is lost within the nanoparticles with a time constant of 146 fs. Ultrafast electron diffraction reveals that this demagnetization is followed by an anisotropic, three-dimensional lattice motion. Analysis of the size, speed, and symmetry of the lattice motion, together with ab initio calculations accounting for the stresses due to electrons and phonons, allow us to reveal the magnetoelastic stress generated by demagnetization.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-343793 (URN)10.1038/s41467-017-02730-7 (DOI)000423430900008 ()29374151 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060EU, Horizon 2020, 737709Swedish National Infrastructure for Computing (SNIC)
Note

Correction in: Nature Communications, vol. 9, article number: 1035. DOI: 10.1038/s41467-018-03389-4

Available from: 2018-03-05 Created: 2018-03-05 Last updated: 2018-07-06Bibliographically approved
Hosen, M. M., Dhakal, G., Dimitri, K., Maldonado, P., Aperis, A., Kabir, F., . . . Neupane, M. (2018). Discovery of topological nodal-line fermionic phase in a magnetic material GdSbTe. Scientific Reports, 8, Article ID 13283.
Open this publication in new window or tab >>Discovery of topological nodal-line fermionic phase in a magnetic material GdSbTe
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2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 13283Article in journal (Refereed) Published
Abstract [en]

Topological Dirac semimetals with accidental band touching between conduction and valence bands protected by time reversal and inversion symmetry are at the frontier of modern condensed matter research. A majority of discovered topological semimetals are nonmagnetic and conserve time reversal symmetry. Here we report the experimental discovery of an antiferromagnetic topological nodal-line semimetallic state in GdSbTe using angle-resolved photoemission spectroscopy. Our systematic study reveals the detailed electronic structure of the paramagnetic state of antiferromagnetic GdSbTe. We observe the presence of multiple Fermi surface pockets including a diamond-shape, and small circular pockets around the zone center and high symmetry X points of the Brillouin zone (BZ), respectively. Furthermore, we observe the presence of a Dirac-like state at the X point of the BZ and the effect of magnetism along the nodal-line direction. Interestingly, our experimental data show a robust  Dirac-like state both below and above the magnetic transition temperature (TN  = 13 K). Having a relatively high transition temperature, GdSbTe provides an archetypical platform to study the interaction between magnetism and topological states of matter.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-359944 (URN)10.1038/s41598-018-31296-7 (DOI)000443746600003 ()30185891 (PubMedID)
Funder
Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC)
Available from: 2018-09-07 Created: 2018-09-07 Last updated: 2018-10-29Bibliographically approved
Maehrlein, S. F., Radu, I., Maldonado, P., Paarmann, A., Gensch, M., Kalashnikova, A. M., . . . Kampfrath, T. (2018). Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation. Science Advances, 4(7), Article ID eaar5164.
Open this publication in new window or tab >>Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation
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2018 (English)In: Science Advances, E-ISSN 2375-2548, Vol. 4, no 7, article id eaar5164Article in journal (Refereed) Published
Abstract [en]

To gain control over magnetic order on ultrafast time scales, a fundamental understanding of the way electron spins interact with the surrounding crystal lattice is required. However, measurement and analysis even of basic collective processes such as spin-phonon equilibration have remained challenging. Here, we directly probe the flow of energy and angular momentum in the model insulating ferrimagnet yttrium iron garnet. After ultrafast resonant lattice excitation, we observe that magnetic order reduces on distinct time scales of 1 ps and 100 ns. Temperature-dependent measurements, a spin-coupling analysis, and simulations show that the two dynamics directly reflect two stages of spin lattice equilibration. On the 1-ps scale, spins and phonons reach quasi-equilibrium in terms of energy through phonon-induced modulation of the exchange interaction. This mechanism leads to identical demagnetization of the ferrimagnet's two spin sublattices and to a previously inaccessible ferrimagnetic state of increased temperature yet unchanged total magnetization. Finally, on the much slower, 100-ns scale, the excess of spin angular momentum is released to the crystal lattice, resulting in full equilibrium. Our findings are relevant for all insulating ferrimagnets and indicate that spin manipulation by phonons, including the spin Seebeck effect, can be extended to antiferromagnets and into the terahertz frequency range.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-364063 (URN)10.1126/sciadv.aar5164 (DOI)000443176100018 ()30027115 (PubMedID)
Funder
EU, Horizon 2020, 681917Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060Swedish National Infrastructure for Computing (SNIC)
Available from: 2018-11-28 Created: 2018-11-28 Last updated: 2018-11-28Bibliographically approved
Hosen, M. M., Dimitri, K., Nandy, A. K., Aperis, A., Sankar, R., Dhakal, G., . . . Neupane, M. (2018). Distinct multiple fermionic states in a single topological metal. Nature Communications, 9, Article ID 3002.
Open this publication in new window or tab >>Distinct multiple fermionic states in a single topological metal
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2018 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 3002Article in journal (Refereed) Published
Abstract [en]

Among the quantum materials that have recently gained interest are the topological insulators, wherein symmetry-protected surface states cross in reciprocal space, and the Dirac nodal-line semimetals, where bulk bands touch along a line in k-space. However, the existence of multiple fermion phases in a single material has not been verified yet. Using angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations, we systematically study the metallic material Hf2Te2P and discover properties, which are unique in a single topological quantum material. We experimentally observe weak topological insulator surface states and our calculations suggest additional strong topological insulator surface states. Our first-principles calculations reveal a one-dimensional Dirac crossing—the surface Dirac-node arc—along a high-symmetry direction which is confirmed by our ARPES measurements. This novel state originates from the surface bands of a weak topological insulator and is therefore distinct from the well-known Fermi arcs in semimetals.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-359978 (URN)10.1038/s41467-018-05233-1 (DOI)000440413500002 ()30068909 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060Swedish National Infrastructure for Computing (SNIC)
Available from: 2018-09-07 Created: 2018-09-07 Last updated: 2018-11-08Bibliographically approved
Noguere, G., Maldonado, P. & De Saint Jean, C. (2018). Doppler broadening of neutron-induced resonances using ab initio phonon spectrum. The European Physical Journal Plus, 133(5), Article ID 177.
Open this publication in new window or tab >>Doppler broadening of neutron-induced resonances using ab initio phonon spectrum
2018 (English)In: The European Physical Journal Plus, ISSN 2190-5444, E-ISSN 2190-5444, Vol. 133, no 5, article id 177Article in journal (Refereed) Published
Abstract [en]

Neutron resonances observed in neutron cross section data can only be compared with their theoretical analogues after a correct broadening of the resonance widths. This broadening is usually carried out by two different theoretical models, namely the Free Gas Model and the Crystal Lattice Model, which, however, are only applicable under certain assumptions. Here, we use neutron transmission experiments on UO2 samples at T = 23.7 K and T = 293.7 K, to investigate the limitations of these models when an ab initio phonon spectrum is introduced in the calculations. Comparisons of the experimental and theoretical transmissions highlight the underestimation of the energy transferred at low temperature and its impact on the accurate determination of the radiation widths Gamma(gamma lambda) of the U-238 resonances lambda. The observed deficiency of the model represents an experimental evidence that the Debye-Waller factor is not correctly calculated at low temperature near the Neel temperature (T-N = 30.8 K).

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-356455 (URN)10.1140/epjp/i2018-12009-y (DOI)000432653000001 ()
Available from: 2018-07-31 Created: 2018-07-31 Last updated: 2018-08-13Bibliographically approved
Gang, S.-g., Adam, R., Plötzing, M., von Witzleben, M., Weier, C., Parlak, U., . . . Oppeneer, P. M. (2018). Element-selective investigation of femtosecond spin dynamics in NiPd magnetic alloys using extreme ultraviolet radiation. Physical Review B, 97(6), Article ID 064412.
Open this publication in new window or tab >>Element-selective investigation of femtosecond spin dynamics in NiPd magnetic alloys using extreme ultraviolet radiation
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 6, article id 064412Article in journal (Refereed) Published
Abstract [en]

We studied femtosecond spin dynamics in NixPd1-x magnetic thin films by optically pumping the system with infrared (1.55 eV) laser pulses and subsequently recording the reflectivity of extreme ultraviolet (XUV) pulses synchronized with the pump pulse train. XUV light in the energy range from 20 to 72 eV was produced by laser high-harmonic generation. The reflectivity of XUV radiation at characteristic resonant energies allowed separate detection of the spin dynamics in the elemental subsystems at the M-2,M-3 absorption edges of Ni (68.0 and 66.2 eV) and N-2,N-3 edges of Pd (55.7 and 50.9 eV). The measurements were performed in transversal magneto-optical Kerr effect geometry. In static measurements, we observed a magnetic signature of the Pd subsystem due to an induced magnetization. Calculated magneto-optical asymmetries based on density functional theory show close agreement with the measured results. Femtosecond spin dynamics measured at the Ni absorption edges indicates that increasing the Pd concentration, which causes a decrease in the Curie temperature T-C, results in a drop of the demagnetization time tau(M), contrary to the tau(M) similar to 1/T-C scaling expected for single-species materials. This observation is ascribed to the increase of the Pd-mediated spin-orbit coupling in the alloy.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-349353 (URN)10.1103/PhysRevB.97.064412 (DOI)000425492100005 ()
Funder
German Research Foundation (DFG), SCHN 353/17-1Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060Swedish National Infrastructure for Computing (SNIC)
Available from: 2018-05-02 Created: 2018-05-02 Last updated: 2018-05-02Bibliographically approved
Hosen, M. M., Dimitri, K., Aperis, A., Maldonado, P., Belopolski, I., Dhakal, G., . . . Neupane, M. (2018). Observation of gapless Dirac surface states in ZrGeTe. Physical Review B, 97(12), Article ID 121103.
Open this publication in new window or tab >>Observation of gapless Dirac surface states in ZrGeTe
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2018 (English)In: Physical Review B, Vol. 97, no 12, article id 121103Article in journal (Refereed) Published
Abstract [en]

The experimental discovery of the topological Dirac semimetal establishes a platform to search for various exotic quantum phases in real materials. ZrSiS-type materials have recently emerged as topological nodal-line semimetals where gapped Dirac-like surface states are observed. Here, we present a systematic angle-resolved photoemission spectroscopy (ARPES) study of ZrGeTe, a nonsymmorphic symmetry protected Dirac semimetal. We observe twoDirac-like gapless surface states at the same <overline> X point of the Brillouin zone. Our theoretical analysis and first-principles calculations reveal that these are protected by crystalline symmetry. Hence, ZrGeTe appears as a rare example of a naturally fine tuned system where the interplay between symmorphic and nonsymmorphic symmetry leads to rich phenomenology and thus opens up opportunities to investigate the physics of Dirac semimetallic and topological insulating phases realized in a single material.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-346602 (URN)10.1103/PhysRevB.97.121103 (DOI)000426779100001 ()
Funder
Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC)
Available from: 2018-03-19 Created: 2018-03-19 Last updated: 2018-05-15Bibliographically approved
Reid, A. H., Shen, X., Maldonado, P., Chase, T., Jal, E., Granitzka, P. W., . . . Dürr, H. A. (2018). Publisher Correction: Beyond a phenomenological description of magnetostriction. Nature Communications, 9, Article ID 1035.
Open this publication in new window or tab >>Publisher Correction: Beyond a phenomenological description of magnetostriction
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2018 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 1035Article in journal (Other academic) Published
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-355826 (URN)10.1038/s41467-018-03389-4 (DOI)000426899700003 ()29515124 (PubMedID)
Note

WoS title: Beyond a phenomenological description of magnetostriction (vol 9, 388, 2018)

Correction to: Nature Communications, vol. 9, article number: 388. DOI: 10.1038/s41467-017-02730-7

Available from: 2018-07-06 Created: 2018-07-06 Last updated: 2018-07-06Bibliographically approved
Balaz, P., Zonda, M., Carva, K., Maldonado, P. & Oppeneer, P. M. (2018). Transport theory for femtosecond laser-induced spin-transfer torques. Journal of Physics: Condensed Matter, 30(11), Article ID 115801.
Open this publication in new window or tab >>Transport theory for femtosecond laser-induced spin-transfer torques
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2018 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 11, article id 115801Article in journal (Refereed) Published
Abstract [en]

Ultrafast demagnetization of magnetic layers pumped by a femtosecond laser pulse is accompanied by a nonthermal spin-polarized current of hot electrons. These spin currents are studied here theoretically in a spin valve with noncollinear magnetizations. To this end, we introduce an extended model of superdiffusive spin transport that enables the treatment of noncollinear magnetic configurations, and apply it to the perpendicular spin valve geometry. We show how spin-transfer torques arise due to this mechanism and calculate their action on the magnetization present, as well as how the latter depends on the thicknesses of the layers and other transport parameters. We demonstrate that there exists a certain optimum thickness of the out-of-plane magnetized spin-current polarizer such that the torque acting on the second magnetic layer is maximal. Moreover, we study the magnetization dynamics excited by the superdiffusive spin-transfer torque due to the flow of hot electrons employing the Landau-Lifshitz-Gilbert equation. Thereby we show that a femtosecond laser pulse applied to one magnetic layer can excite small-angle precessions of the magnetization in the second magnetic layer. We compare our calculations with recent experimental results.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
ultrafast demagnetization, spin transfer torque, magnetization dynamics, spin current, spin transport
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-350487 (URN)10.1088/1361-648X/aaad95 (DOI)000425996100001 ()
Funder
Swedish National Infrastructure for Computing (SNIC)Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC)EU, Horizon 2020, 737709Knut and Alice Wallenberg Foundation, 2015.0060
Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2018-05-17Bibliographically approved
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