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Bobowski K, Zheng X, Frietsch B, Lawrenz D, Bronsch W, Gahl C, Andres B, Strüber C, Carley R, Teichmann M, Scherz A, Molodtsov S, Cacho C, Chapman RT, Springate E, Weinelt M. Ultrafast spin transfer and its impact on the electronic structure. SCIENCE ADVANCES 2024; 10:eadn4613. [PMID: 39018415 PMCID: PMC466954 DOI: 10.1126/sciadv.adn4613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Accepted: 06/12/2024] [Indexed: 07/19/2024]
Abstract
Optically induced intersite spin transfer (OISTR) promises manipulation of spin systems within the ultimate time limit of laser excitation. Following its prediction, signatures of ultrafast spin transfer between oppositely aligned spin sublattices have been observed in magnetic alloys and multilayers. However, it is known neither from theory nor from experiment whether the band structure immediately follows the ultrafast change in spin polarization or whether the exchange split bands remain rigid. We show that ultrafast spin transfer occurs even in ferromagnetic gadolinium metal. Charge transfer between localized surface and extended valence-band states leads to a decrease of the surface spin polarization. This synchronously alters the exchange splitting of the bulk valence bands during laser excitation. Moreover, the onset of demagnetization can be tuned by over 200 fs by changing the temperature-dependent spin mixing. Our results show a promising route to ultrafast control of the magnetization, widening the impact and applicability of OISTR.
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Affiliation(s)
- Kamil Bobowski
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Xinwei Zheng
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Björn Frietsch
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Dominic Lawrenz
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Wibke Bronsch
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
- Elettra-Sincrotrone Trieste S.C.p.A., Strada Statale 14 - km 163.5 in AREA Science Park, 34149 Basovizza, Trieste, Italy
| | - Cornelius Gahl
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Beatrice Andres
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Christian Strüber
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Robert Carley
- European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany
| | | | - Andreas Scherz
- European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Serguei Molodtsov
- European XFEL GmbH, Holzkoppel 4, 22869 Schenefeld, Germany
- Institute of Experimental Physics, TU Bergakademie Freiberg, Leipziger Str. 23, 09599 Freiberg, Germany
| | | | | | | | - Martin Weinelt
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
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Zhang GP, Jenkins T, Bennett M, Bai YH. Manifestation of intra-atomic 5d6s-4f exchange coupling in photoexcited gadolinium. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:495807. [PMID: 29105644 DOI: 10.1088/1361-648x/aa986c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Intra-atomic exchange couplings (IECs) between 5d6s and 4f electrons are ubiquitous in rare-earth metals and play a critical role in spin dynamics. However, detecting them in real time domain has been difficult. Here we show the direct evidence of IEC between 5d6s and 4f electrons in gadolinium. Upon femtosecond laser excitation, 5d6s electrons are directly excited; their majority bands shift toward the Fermi level while their minority bands do the opposite. For the first time, our first-principles minority shift now agrees with the experiment quantitatively. Excited 5d6s electrons lower the exchange potential barrier for 4f electrons, so the 4f states are also shifted in energy, a prediction that can be tested experimentally. Although a significant number of 5d6s electrons, some several eV below the Fermi level, are excited out of the Fermi sea, there is no change in the 4f states, a clear manifestation of intra-atomic exchange coupling.
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Affiliation(s)
- G P Zhang
- Department of Physics, Indiana State University, Terre Haute, IN 47809, United States of America
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3
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Nghiem HTM, Costi TA. Time Evolution of the Kondo Resonance in Response to a Quench. PHYSICAL REVIEW LETTERS 2017; 119:156601. [PMID: 29077442 DOI: 10.1103/physrevlett.119.156601] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Indexed: 05/26/2023]
Abstract
We investigate the time evolution of the Kondo resonance in response to a quench by applying the time-dependent numerical renormalization group (TDNRG) approach to the Anderson impurity model in the strong correlation limit. For this purpose, we derive within the TDNRG approach a numerically tractable expression for the retarded two-time nonequilibrium Green function G(t+t^{'},t), and its associated time-dependent spectral function, A(ω,t), for times t both before and after the quench. Quenches from both mixed valence and Kondo correlated initial states to Kondo correlated final states are considered. For both cases, we find that the Kondo resonance in the zero temperature spectral function, a preformed version of which is evident at very short times t→0^{+}, only fully develops at very long times t≳1/T_{K}, where T_{K} is the Kondo temperature of the final state. In contrast, the final state satellite peaks develop on a fast time scale 1/Γ during the time interval -1/Γ≲t≲+1/Γ, where Γ is the hybridization strength. Initial and final state spectral functions are recovered in the limits t→-∞ and t→+∞, respectively. Our formulation of two-time nonequilibrium Green functions within the TDNRG approach provides a first step towards using this method as an impurity solver within nonequilibrium dynamical mean field theory.
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Affiliation(s)
- H T M Nghiem
- Peter Grünberg Institut and Institute for Advanced Simulation, Research Centre Jülich, 52425 Jülich, Germany
- Advanced Institute for Science and Technology, Hanoi University of Science and Technology, 10000 Hanoi, Vietnam
| | - T A Costi
- Peter Grünberg Institut and Institute for Advanced Simulation, Research Centre Jülich, 52425 Jülich, Germany
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Andres B, Christ M, Gahl C, Wietstruk M, Weinelt M, Kirschner J. Separating Exchange Splitting from Spin Mixing in Gadolinium by Femtosecond Laser Excitation. PHYSICAL REVIEW LETTERS 2015; 115:207404. [PMID: 26613472 DOI: 10.1103/physrevlett.115.207404] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Indexed: 06/05/2023]
Abstract
Employing spin-, time-, and energy-resolved photoemission spectroscopy, we present the first study on the spin polarization of a single electronic state after ultrafast optical excitation. Our investigation concentrates on the majority-spin component of the d-band-derived Gd(0001) surface state d(z(2))(↑). While its binding energy shows a rapid Stoner-like shift by 90 meV with an exponential time constant of τ(E)=0.6±0.1 ps, the d(z(2))(↑) spin polarization remains nearly constant within the first picoseconds and decays with τ(S)=15±8 ps. This behavior is in clear contrast to the equilibrium phase transition, where the spin polarization vanishes at the Curie temperature.
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Affiliation(s)
- Beatrice Andres
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Marc Christ
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Cornelius Gahl
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Marko Wietstruk
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Martin Weinelt
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Jürgen Kirschner
- Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle/Saale, Germany
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Frietsch B, Bowlan J, Carley R, Teichmann M, Wienholdt S, Hinzke D, Nowak U, Carva K, Oppeneer PM, Weinelt M. Disparate ultrafast dynamics of itinerant and localized magnetic moments in gadolinium metal. Nat Commun 2015; 6:8262. [PMID: 26355196 PMCID: PMC4579838 DOI: 10.1038/ncomms9262] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Accepted: 08/04/2015] [Indexed: 01/26/2023] Open
Abstract
The Heisenberg–Dirac intra-atomic exchange coupling is responsible for the formation of the atomic spin moment and thus the strongest interaction in magnetism. Therefore, it is generally assumed that intra-atomic exchange leads to a quasi-instantaneous aligning process in the magnetic moment dynamics of spins in separate, on-site atomic orbitals. Following ultrashort optical excitation of gadolinium metal, we concurrently record in photoemission the 4f magnetic linear dichroism and 5d exchange splitting. Their dynamics differ by one order of magnitude, with decay constants of 14 versus 0.8 ps, respectively. Spin dynamics simulations based on an orbital-resolved Heisenberg Hamiltonian combined with first-principles calculations explain the particular dynamics of 5d and 4f spin moments well, and corroborate that the 5d exchange splitting traces closely the 5d spin-moment dynamics. Thus gadolinium shows disparate dynamics of the localized 4f and the itinerant 5d spin moments, demonstrating a breakdown of their intra-atomic exchange alignment on a picosecond timescale. Due the strength of the intra-atomic exchange interaction, it is generally assumed that alignment of spin moments in intra-atomic orbitals is quasi-instantaneous. Here, the authors demonstrate the breakdown of this relation between the 4f and 5d electrons in gadolinium following ultrashort optical excitation.
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Affiliation(s)
- B Frietsch
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.,Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin, Germany
| | - J Bowlan
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.,Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin, Germany
| | - R Carley
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.,Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin, Germany
| | - M Teichmann
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.,Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin, Germany
| | - S Wienholdt
- Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
| | - D Hinzke
- Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
| | - U Nowak
- Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany
| | - K Carva
- Department of Physics and Astronomy, Uppsala University, PO Box 516, 75120 Uppsala, Sweden.,Charles University, Faculty of Mathematics and Physics, DCMP, Ke Karlovu 5, CZ-12116 Prague 2, Czech Republic
| | - P M Oppeneer
- Department of Physics and Astronomy, Uppsala University, PO Box 516, 75120 Uppsala, Sweden
| | - M Weinelt
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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Avigo I, Cortés R, Rettig L, Thirupathaiah S, Jeevan HS, Gegenwart P, Wolf T, Ligges M, Wolf M, Fink J, Bovensiepen U. Coherent excitations and electron-phonon coupling in Ba/EuFe2As2 compounds investigated by femtosecond time- and angle-resolved photoemission spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:094003. [PMID: 23399984 DOI: 10.1088/0953-8984/25/9/094003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We employed femtosecond time- and angle-resolved photoelectron spectroscopy to analyze the response of the electronic structure of the 122 Fe-pnictide parent compounds Ba/EuFe(2)As(2) and optimally doped BaFe(1.85)Co(0.15)As(2) near the Γ point to optical excitation by an infrared femtosecond laser pulse. We identify pronounced changes of the electron population within several 100 meV above and below the Fermi level, which we explain as a combination of (i) coherent lattice vibrations, (ii) a hot electron and hole distribution, and (iii) transient modifications of the chemical potential. The responses of the three different materials are very similar. In the coherent response we identify three modes at 5.6, 3.3, and 2.6 THz. While the highest frequency mode is safely assigned to the A(1g) mode, the other two modes require a discussion in comparison to the literature. Employing a transient three temperature model we deduce from the transient evolution of the electron distribution a rather weak, momentum-averaged electron-phonon coupling quantified by values for λ<ω(2)> between 30 and 70 meV(2). The chemical potential is found to present pronounced transient changes reaching a maximum of 15 meV about 0.6 ps after optical excitation and is modulated by the coherent phonons. This change in the chemical potential is particularly strong in a multiband system like the 122 Fe-pnictide compounds investigated here due to the pronounced variation of the electron density of states close to the equilibrium chemical potential.
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Affiliation(s)
- I Avigo
- Fakultät für Physik, Universität Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany
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Carley R, Döbrich K, Frietsch B, Gahl C, Teichmann M, Schwarzkopf O, Wernet P, Weinelt M. Femtosecond laser excitation drives ferromagnetic gadolinium out of magnetic equilibrium. PHYSICAL REVIEW LETTERS 2012; 109:057401. [PMID: 23006205 DOI: 10.1103/physrevlett.109.057401] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Indexed: 06/01/2023]
Abstract
The temporal evolution of the exchange-split Δ(2)-like Σ valence bands of the 4f-ferromagnet gadolinium after femtosecond laser excitation has been studied using angle-resolved photoelectron spectroscopy based on high-order harmonic generation. The ultrafast drop of the exchange splitting reflects the magnetic response seen in femtosecond magnetic dichroism experiments. However, while the minority valence band reacts immediately, the response of the majority counterpart is delayed by 1 picosecond and is only half as fast. These findings demonstrate that laser excitation drives the valence band structure out of magnetic equilibrium.
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Koopmans B, Malinowski G, Dalla Longa F, Steiauf D, Fähnle M, Roth T, Cinchetti M, Aeschlimann M. Explaining the paradoxical diversity of ultrafast laser-induced demagnetization. NATURE MATERIALS 2010; 9:259-65. [PMID: 20010830 DOI: 10.1038/nmat2593] [Citation(s) in RCA: 234] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Accepted: 11/03/2009] [Indexed: 05/22/2023]
Abstract
Pulsed-laser-induced quenching of ferromagnetic order has intrigued researchers since pioneering works in the 1990s. It was reported that demagnetization in gadolinium proceeds within 100 ps, but three orders of magnitude faster in ferromagnetic transition metals such as nickel. Here we show that a model based on electron-phonon-mediated spin-flip scattering explains both timescales on equal footing. Our interpretation is supported by ab initio estimates of the spin-flip scattering probability, and experimental fluence dependencies are shown to agree perfectly with predictions. A phase diagram is constructed in which two classes of laser-induced magnetization dynamics can be distinguished, where the ratio of the Curie temperature to the atomic magnetic moment turns out to have a crucial role. We conclude that the ultrafast magnetization dynamics can be well described disregarding highly excited electronic states, merely considering the thermalized electron system.
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Affiliation(s)
- B Koopmans
- Department of Applied Physics, Center for NanoMaterials (cNM), Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
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Schmitt F, Kirchmann PS, Bovensiepen U, Moore RG, Rettig L, Krenz M, Chu JH, Ru N, Perfetti L, Lu DH, Wolf M, Fisher IR, Shen ZX. Transient electronic structure and melting of a charge density wave in TbTe3. Science 2008; 321:1649-52. [PMID: 18703710 DOI: 10.1126/science.1160778] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Obtaining insight into microscopic cooperative effects is a fascinating topic in condensed matter research because, through self-coordination and collectivity, they can lead to instabilities with macroscopic impacts like phase transitions. We used femtosecond time- and angle-resolved photoelectron spectroscopy (trARPES) to optically pump and probe TbTe3, an excellent model system with which to study these effects. We drove a transient charge density wave melting, excited collective vibrations in TbTe3, and observed them through their time-, frequency-, and momentum-dependent influence on the electronic structure. We were able to identify the role of the observed collective vibration in the transition and to document the transition in real time. The information that we demonstrate as being accessible with trARPES will greatly enhance the understanding of all materials exhibiting collective phenomena.
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Affiliation(s)
- F Schmitt
- Department of Applied Physics, Via Pueblo Mall, Stanford University, Stanford, CA 94305, USA
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