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Subpicosecond metamagnetic phase transition in FeRh driven by non-equilibrium electron dynamics. Nat Commun 2021; 12:5088. [PMID: 34429414 PMCID: PMC8384879 DOI: 10.1038/s41467-021-25347-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Accepted: 07/22/2021] [Indexed: 11/11/2022] Open
Abstract
Femtosecond light-induced phase transitions between different macroscopic orders provide the possibility to tune the functional properties of condensed matter on ultrafast timescales. In first-order phase transitions, transient non-equilibrium phases and inherent phase coexistence often preclude non-ambiguous detection of transition precursors and their temporal onset. Here, we present a study combining time-resolved photoelectron spectroscopy and ab-initio electron dynamics calculations elucidating the transient subpicosecond processes governing the photoinduced generation of ferromagnetic order in antiferromagnetic FeRh. The transient photoemission spectra are accounted for by assuming that not only the occupation of electronic states is modified during the photoexcitation process. Instead, the photo-generated non-thermal distribution of electrons modifies the electronic band structure. The ferromagnetic phase of FeRh, characterized by a minority band near the Fermi energy, is established 350 ± 30 fs after the laser excitation. Ab-initio calculations indicate that the phase transition is initiated by a photoinduced Rh-to-Fe charge transfer. In FeRh, it is possible to optically drive a phase transition between ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering. Here, using a combination of photoelectron spectroscopy and ab-initio calculations, the authors demonstrate the existence of a transient intermediate phase, explaining the delayed appearance of the FM phase.
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Li J, Ma J, Du K, Zhao E, Guo J, Mao J, Ling T. Double exchange interaction promoted high-valence metal sites for neutral oxygen evolution reaction. Chem Commun (Camb) 2020; 56:15004-15007. [PMID: 33185208 DOI: 10.1039/d0cc06453j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A unique double-exchange strategy is adopted to access active high-valent transition metal sites during neutral oxygen evolution reaction (OER). This double-exchange is realized through electronic interaction between transition metal ions and foreign dopants in a transition metal oxide. Based on systematical evaluation on dopants with varied d-electron numbers, we demonstrate that the d electron-poor dopant exhibits more significant double-exchange interaction with the transition metal ions, and therefore obtains more active high-valence metal sites, and thus achieves better neutral OER performance.
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Affiliation(s)
- Jisi Li
- Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science and Engineering, Tianjin University, Tianjin, 300072, China.
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Gillmeister K, Golež D, Chiang CT, Bittner N, Pavlyukh Y, Berakdar J, Werner P, Widdra W. Ultrafast coupled charge and spin dynamics in strongly correlated NiO. Nat Commun 2020; 11:4095. [PMID: 32796844 PMCID: PMC7429846 DOI: 10.1038/s41467-020-17925-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 07/17/2020] [Indexed: 11/30/2022] Open
Abstract
Charge excitations across an electronic band gap play an important role in opto-electronics and light harvesting. In contrast to conventional semiconductors, studies of above-band-gap photoexcitations in strongly correlated materials are still in their infancy. Here we reveal the ultrafast dynamics controlled by Hund’s physics in strongly correlated photoexcited NiO. By combining time-resolved two-photon photoemission experiments with state-of-the-art numerical calculations, an ultrafast (≲10 fs) relaxation due to Hund excitations and related photo-induced in-gap states are identified. Remarkably, the weight of these in-gap states displays long-lived coherent THz oscillations up to 2 ps at low temperature. The frequency of these oscillations corresponds to the strength of the antiferromagnetic superexchange interaction in NiO and their lifetime vanishes slightly above the Néel temperature. Numerical simulations of a two-band t-J model reveal that the THz oscillations originate from the interplay between local many-body excitations and antiferromagnetic spin correlations. Nickel Oxide (NiO) is a strongly correlated insulator with antiferromagnetic (AFM) ordering. Here, using pump-probe photoemission on NiO, the authors observe coherent terahertz oscillations in the photoemission signal, a signature of an in-gap state coupled to the AFM background.
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Affiliation(s)
- Konrad Gillmeister
- Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, 06120, Halle, Germany
| | - Denis Golež
- Center for Computational Quantum Physics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA.,Department of Physics, University of Fribourg, 1700, Fribourg, Switzerland
| | - Cheng-Tien Chiang
- Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, 06120, Halle, Germany
| | - Nikolaj Bittner
- Department of Physics, University of Fribourg, 1700, Fribourg, Switzerland
| | - Yaroslav Pavlyukh
- Department of Physics, Technische Universität Kaiserslautern, 67653, Kaiserslautern, Germany
| | - Jamal Berakdar
- Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, 06120, Halle, Germany
| | - Philipp Werner
- Department of Physics, University of Fribourg, 1700, Fribourg, Switzerland.
| | - Wolf Widdra
- Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, 06120, Halle, Germany. .,Max Planck Institute of Microstructure Physics, 06120, Halle, Germany.
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Ishizuka H, Sato M. Rectification of Spin Current in Inversion-Asymmetric Magnets with Linearly Polarized Electromagnetic Waves. PHYSICAL REVIEW LETTERS 2019; 122:197702. [PMID: 31144955 DOI: 10.1103/physrevlett.122.197702] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2018] [Revised: 02/04/2019] [Indexed: 06/09/2023]
Abstract
We theoretically propose a method of rectifying spin current with a linearly polarized electromagnetic wave in inversion-asymmetric magnetic insulators. To demonstrate the proposal, we consider quantum spin chains as a simple example; these models are mapped to fermion (spinon) models via Jordan-Wigner transformation. Using a nonlinear response theory, we find that a dc spin current is generated by the linearly polarized waves. The spin current shows rich anisotropic behavior depending on the direction of the electromagnetic wave. This is a manifestation of the rich interplay between spins and the waves; inverse Dzyaloshinskii-Moriya, Zeeman, and magnetostriction couplings lead to different behaviors of the spin current. The resultant spin current is insensitive to the relaxation time of spinons, a property of which potentially benefits a long-distance propagation of the spin current. An estimate of the required electromagnetic wave is given.
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Affiliation(s)
- Hiroaki Ishizuka
- Department of Applied Physics, The University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
| | - Masahiro Sato
- Department of Physics, Ibaraki University, Mito, Ibaraki 310-8512, Japan
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Liu H, Sun JT, Liu M, Meng S. Screening Magnetic Two-Dimensional Atomic Crystals with Nontrivial Electronic Topology. J Phys Chem Lett 2018; 9:6709-6715. [PMID: 30403873 DOI: 10.1021/acs.jpclett.8b02783] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
To date, only a few two-dimensional (2D) magnetic crystals have been experimentally confirmed, such as CrI3 and CrGeTe3, all with very low Curie temperatures ( TC). High-throughput first-principles screening over a large set of materials yields 89 magnetic monolayers including 56 ferromagnetic (FM) and 33 antiferromagnetic compounds. Among them, 24 FM monolayers are promising candidates possessing TC higher than that of CrI3. High TC monolayers with fascinating electronic phases are identified: (i) quantum anomalous Hall and valley Hall effects coexist in a single material RuCl3 or VCl3, leading to a valley-polarized quantum anomalous Hall state; (ii) TiBr3, Co2NiO6, and V2H3O5 are revealed to be half-metals. More importantly, a new type of fermion dubbed type-II Weyl ring is discovered in ScCl. Our work provides a database of 2D magnetic materials, which could guide experimental realization of high-temperature magnetic monolayers with exotic electronic states for future spintronics and quantum computing applications.
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Affiliation(s)
- Hang Liu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , People's Republic of China
- University of Chinese Academy of Sciences , Beijing 100049 , People's Republic of China
| | - Jia-Tao Sun
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , People's Republic of China
- University of Chinese Academy of Sciences , Beijing 100049 , People's Republic of China
| | - Miao Liu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , People's Republic of China
| | - Sheng Meng
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics , Chinese Academy of Sciences , Beijing 100190 , People's Republic of China
- Collaborative Innovation Center of Quantum Matter , Beijing 100190 , People's Republic of China
- University of Chinese Academy of Sciences , Beijing 100049 , People's Republic of China
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