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Warshauer JA, Bustamante Lopez DA, Dong Q, Chen G, Hu W. Transient gap generation in BaFe 2As 2 driven by coherent lattice vibrations. PNAS NEXUS 2023; 2:pgad164. [PMID: 37266397 PMCID: PMC10230283 DOI: 10.1093/pnasnexus/pgad164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 05/02/2023] [Accepted: 05/08/2023] [Indexed: 06/03/2023]
Abstract
Iron-based superconductors provide a rich platform to investigate the interplay between unconventional superconductivity, nematicity, and magnetism. The electronic structure and the magnetic properties of iron-based superconductors are highly sensitive to the pnictogen height. Coherent excitation of the A1g phonon by femtosecond laser directly modulates the pnictogen height, which has been used to control the physical properties of iron-based superconductors. Previous studies show that the driven A1g phonon resulted in a transient increase of the pnictogen height in BaFe2As2, favoring an enhanced Fe magnetic moment. However, there are no direct observations on either the enhanced Fe magnetic moments or the enhanced spin-density wave (SDW) gap. Here, we use time-resolved broadband terahertz spectroscopy to investigate the dynamics of BaFe2As2 in the A1g phonon-driven state. Below the SDW transition temperature, we observe a transient gap generation at early-time delays. A similar transient feature is observed in the normal state up to room temperature.
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Affiliation(s)
- Jacob A Warshauer
- Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, 02215 MA, USA
| | | | - Qingxin Dong
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, 8 Zhongguancun 3rd South Street, 100190 Beijing, China
- School of Physical Sciences, University of Chinese Academy of Sciences, No. 19 A Yuquan Road, 100049 Beijing, China
| | - Genfu Chen
- Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, 8 Zhongguancun 3rd South Street, 100190 Beijing, China
- School of Physical Sciences, University of Chinese Academy of Sciences, No. 19 A Yuquan Road, 100049 Beijing, China
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2
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Bao C, Li Q, Xu S, Zhou S, Zeng XY, Zhong H, Gao Q, Luo L, Sun D, Xia TL, Zhou S. Population Inversion and Dirac Fermion Cooling in 3D Dirac Semimetal Cd 3As 2. NANO LETTERS 2022; 22:1138-1144. [PMID: 35050626 DOI: 10.1021/acs.nanolett.1c04250] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Revealing the ultrafast dynamics of three-dimensional (3D) Dirac fermions is critical for both fundamental science and device applications. So far, how the cooling of 3D Dirac fermions differs from that of two-dimensional (2D) and whether there is population inversion are fundamental questions to be answered. Here we reveal the ultrafast dynamics of Dirac fermions in a model 3D Dirac semimetal Cd3As2 by time- and angle-resolved photoemission spectroscopy with a tunable probe photon energy. The energy- and momentum-resolved relaxation rate shows a linear dependence on the energy, suggesting Dirac fermion cooling through intraband relaxation. Moreover, a population inversion is reported based on the observation of accumulated photoexcited carriers in the conduction band with a lifetime of 3.0 ps. Our work provides direct experimental evidence for a long-lived population inversion in a 3D Dirac semimetal, which is in contrast to 2D graphene with a much shorter lifetime.
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Affiliation(s)
- Changhua Bao
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P. R. China
| | - Qian Li
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P. R. China
| | - Sheng Xu
- Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, P. R. China
| | - Shaohua Zhou
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P. R. China
| | - Xiang-Yu Zeng
- Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, P. R. China
| | - Haoyuan Zhong
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P. R. China
| | - Qixuan Gao
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P. R. China
| | - Laipeng Luo
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P. R. China
| | - Dong Sun
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P. R. China
| | - Tian-Long Xia
- Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, P. R. China
| | - Shuyun Zhou
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, P. R. China
- Frontier Science Center for Quantum Information, Beijing 100084, P. R. China
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3
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Yang Y, Tang T, Duan S, Zhou C, Hao D, Zhang W. A time- and angle-resolved photoemission spectroscopy with probe photon energy up to 6.7 eV. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2019; 90:063905. [PMID: 31254991 DOI: 10.1063/1.5090439] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Accepted: 06/04/2019] [Indexed: 06/09/2023]
Abstract
We present the development of a time- and angle-resolved photoemission spectroscopy based on a Yb-based femtosecond laser and a hemispherical electron analyzer. The energy of the pump photon is tunable between 1.4 and 1.9 eV, and the pulse duration is around 30 fs. We use a KBe2BO3F2 nonlinear optical crystal to generate probe pulses, of which the photon energy is up to 6.7 eV, and obtain an overall time resolution of 1 ps and energy resolution of 18 meV. In addition, β-BaB2O4 crystals are used to generate alternative probe pulses at 6.05 eV, giving an overall time resolution of 130 fs and energy resolution of 19 meV. We illustrate the performance of the system with representative data on several samples (Bi2Se3, YbCd2Sb2, and FeSe).
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Affiliation(s)
- Yuanyuan Yang
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Tianwei Tang
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Shaofeng Duan
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Chaocheng Zhou
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Duxing Hao
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Wentao Zhang
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
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Shimojima T, Suzuki Y, Nakamura A, Mitsuishi N, Kasahara S, Shibauchi T, Matsuda Y, Ishida Y, Shin S, Ishizaka K. Ultrafast nematic-orbital excitation in FeSe. Nat Commun 2019; 10:1946. [PMID: 31036846 PMCID: PMC6488589 DOI: 10.1038/s41467-019-09869-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2018] [Accepted: 03/30/2019] [Indexed: 11/24/2022] Open
Abstract
The electronic nematic phase is an unconventional state of matter that spontaneously breaks the rotational symmetry of electrons. In iron-pnictides/chalcogenides and cuprates, the nematic ordering and fluctuations have been suggested to have as-yet-unconfirmed roles in superconductivity. However, most studies have been conducted in thermal equilibrium, where the dynamical property and excitation can be masked by the coupling with the lattice. Here we use femtosecond optical pulse to perturb the electronic nematic order in FeSe. Through time-, energy-, momentum- and orbital-resolved photo-emission spectroscopy, we detect the ultrafast dynamics of electronic nematicity. In the strong-excitation regime, through the observation of Fermi surface anisotropy, we find a quick disappearance of the nematicity followed by a heavily-damped oscillation. This short-life nematicity oscillation is seemingly related to the imbalance of Fe 3dxz and dyz orbitals. These phenomena show critical behavior as a function of pump fluence. Our real-time observations reveal the nature of the electronic nematic excitation instantly decoupled from the underlying lattice. Several experiments have shown evidence for unusual nematic electronic behaviour in unconventional superconductors. Here the authors use pump-probe spectroscopy to observe out-of-equilibrium behaviour of coupled nematic-orbital excitations in iron selenide.
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Affiliation(s)
- T Shimojima
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan. .,Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, The University of Tokyo, Tokyo, 113-8656, Japan.
| | - Y Suzuki
- Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, The University of Tokyo, Tokyo, 113-8656, Japan
| | - A Nakamura
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan.,Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, The University of Tokyo, Tokyo, 113-8656, Japan
| | - N Mitsuishi
- Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, The University of Tokyo, Tokyo, 113-8656, Japan
| | - S Kasahara
- Department of Physics, Kyoto University, Kyoto, 606-8502, Japan
| | - T Shibauchi
- Department of Advanced Materials Science, The University of Tokyo, Kashiwa, 277-8561, Japan
| | - Y Matsuda
- Department of Physics, Kyoto University, Kyoto, 606-8502, Japan
| | - Y Ishida
- Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, 277-8581, Japan
| | - S Shin
- Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, 277-8581, Japan
| | - K Ishizaka
- RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan.,Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, The University of Tokyo, Tokyo, 113-8656, Japan
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5
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Zhou X, He S, Liu G, Zhao L, Yu L, Zhang W. New developments in laser-based photoemission spectroscopy and its scientific applications: a key issues review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:062101. [PMID: 29460857 DOI: 10.1088/1361-6633/aab0cc] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The significant progress in angle-resolved photoemission spectroscopy (ARPES) in last three decades has elevated it from a traditional band mapping tool to a precise probe of many-body interactions and dynamics of quasiparticles in complex quantum systems. The recent developments of deep ultraviolet (DUV, including ultraviolet and vacuum ultraviolet) laser-based ARPES have further pushed this technique to a new level. In this paper, we review some latest developments in DUV laser-based photoemission systems, including the super-high energy and momentum resolution ARPES, the spin-resolved ARPES, the time-of-flight ARPES, and the time-resolved ARPES. We also highlight some scientific applications in the study of electronic structure in unconventional superconductors and topological materials using these state-of-the-art DUV laser-based ARPES. Finally we provide our perspectives on the future directions in the development of laser-based photoemission systems.
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Affiliation(s)
- Xingjiang Zhou
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China. Collaborative Innovation Center of Quantum Matter, Beijing 100871, People's Republic of China
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6
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Zapf S, Dressel M. Europium-based iron pnictides: a unique laboratory for magnetism, superconductivity and structural effects. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2017; 80:016501. [PMID: 27811393 DOI: 10.1088/0034-4885/80/1/016501] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Despite decades of intense research, the origin of high-temperature superconductivity in cuprates and iron-based compounds is still a mystery. Magnetism and superconductivity are traditionally antagonistic phenomena; nevertheless, there is basically no doubt left that unconventional superconductivity is closely linked to magnetism. But this is not the whole story; recently, also structural effects related to the so-called nematic phase gained considerable attention. In order to obtain more information about this peculiar interplay, systematic material research is one of the most important attempts, revealing from time to time unexpected effects. Europium-based iron pnictides are the latest example of such a completely paradigmatic material, as they display not only spin-density-wave and superconducting ground states, but also local Eu2+ magnetism at a similar temperature scale. Here we review recent experimental progress in determining the complex phase diagrams of europium-based iron pnictides. The conclusions drawn from the observations reach far beyond these model systems. Thus, although europium-based iron pnictides are very peculiar, they provide a unique platform to study the common interplay of structural-nematic, magnetic and electronic effects in high-temperature superconductors.
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Affiliation(s)
- Sina Zapf
- 1 Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
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7
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Rettig L, Dornes C, Thielemann-Kühn N, Pontius N, Zabel H, Schlagel DL, Lograsso TA, Chollet M, Robert A, Sikorski M, Song S, Glownia JM, Schüßler-Langeheine C, Johnson SL, Staub U. Itinerant and Localized Magnetization Dynamics in Antiferromagnetic Ho. PHYSICAL REVIEW LETTERS 2016; 116:257202. [PMID: 27391747 DOI: 10.1103/physrevlett.116.257202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Indexed: 05/19/2023]
Abstract
Using femtosecond time-resolved resonant magnetic x-ray diffraction at the Ho L_{3} absorption edge, we investigate the demagnetization dynamics in antiferromagnetically ordered metallic Ho after femtosecond optical excitation. Tuning the x-ray energy to the electric dipole (E1, 2p→5d) or quadrupole (E2, 2p→4f) transition allows us to selectively and independently study the spin dynamics of the itinerant 5d and localized 4f electronic subsystems via the suppression of the magnetic (2 1 3-τ) satellite peak. We find demagnetization time scales very similar to ferromagnetic 4f systems, suggesting that the loss of magnetic order occurs via a similar spin-flip process in both cases. The simultaneous demagnetization of both subsystems demonstrates strong intra-atomic 4f-5d exchange coupling. In addition, an ultrafast lattice contraction due to the release of magneto-striction leads to a transient shift of the magnetic satellite peak.
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Affiliation(s)
- L Rettig
- Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
- Current Address: Abteilung Physikalische Chemie, Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin, Germany
| | - C Dornes
- Institute for Quantum Electronics, Physics Department, ETH Zürich, 8093 Zürich, Switzerland
| | - N Thielemann-Kühn
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Straße 15, 12489 Berlin, Germany
- Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Straße 24/25, 14476 Potsdam-Golm, Germany
| | - N Pontius
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - H Zabel
- Institute for Experimental Physics, Ruhr-Universität Bochum, 44780 Bochum, Germany
| | - D L Schlagel
- Division of Materials Sciences and Engineering, Ames Laboratory, Ames, Iowa 50011, USA
| | - T A Lograsso
- Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA
| | - M Chollet
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - A Robert
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - M Sikorski
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - S Song
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - J M Glownia
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - C Schüßler-Langeheine
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - S L Johnson
- Institute for Quantum Electronics, Physics Department, ETH Zürich, 8093 Zürich, Switzerland
| | - U Staub
- Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
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8
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Rettig L, Mariager SO, Ferrer A, Grübel S, Johnson JA, Rittmann J, Wolf T, Johnson SL, Ingold G, Beaud P, Staub U. Ultrafast structural dynamics of the orthorhombic distortion in the Fe-pnictide parent compound BaFe2As2. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2016; 3:023611. [PMID: 27158636 PMCID: PMC4841800 DOI: 10.1063/1.4947250] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 04/09/2016] [Indexed: 05/19/2023]
Abstract
Using femtosecond time-resolved hard x-ray diffraction, we investigate the structural dynamics of the orthorhombic distortion in the Fe-pnictide parent compound BaFe2As2. The orthorhombic distortion analyzed by the transient splitting of the (1 0 3) Bragg reflection is suppressed on an initial timescale of 35 ps, which is much slower than the suppression of magnetic and nematic order. This observation demonstrates a transient state with persistent structural distortion and suppressed magnetic/nematic order which are strongly linked in thermal equilibrium. We suggest a way of quantifying the coupling between structural and nematic degrees of freedom based on the dynamics of the respective order parameters.
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Affiliation(s)
- L Rettig
- Swiss Light Source, Paul Scherrer Institut , CH-5232 Villigen PSI, Switzerland
| | - S O Mariager
- Swiss Light Source, Paul Scherrer Institut , CH-5232 Villigen PSI, Switzerland
| | | | - S Grübel
- Swiss Light Source, Paul Scherrer Institut , CH-5232 Villigen PSI, Switzerland
| | - J A Johnson
- Swiss Light Source, Paul Scherrer Institut , CH-5232 Villigen PSI, Switzerland
| | | | - T Wolf
- Karlsruhe Institute of Technology , Institut für Festkörperphysik, D-76021 Karlsruhe, Germany
| | - S L Johnson
- Institute for Quantum Electronics, ETH Zürich , CH-8093 Zürich, Switzerland
| | | | | | - U Staub
- Swiss Light Source, Paul Scherrer Institut , CH-5232 Villigen PSI, Switzerland
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9
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Rettig L, Mariager SO, Ferrer A, Grübel S, Johnson JA, Rittmann J, Wolf T, Johnson SL, Ingold G, Beaud P, Staub U. Ultrafast structural dynamics of the Fe-pnictide parent compound BaFe(2)As(2). PHYSICAL REVIEW LETTERS 2015; 114:067402. [PMID: 25723244 DOI: 10.1103/physrevlett.114.067402] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Indexed: 05/19/2023]
Abstract
Using femtosecond time-resolved x-ray diffraction we investigate the structural dynamics of the coherently excited A(1g) phonon mode in the Fe-pnictide parent compound BaFe(2)As(2). The fluence dependent intensity oscillations of two specific Bragg reflections with distinctly different sensitivity to the pnictogen height in the compound allow us to quantify the coherent modifications of the Fe-As tetrahedra, indicating a transient increase of the Fe magnetic moments. By a comparison with time-resolved photoemission data, we derive the electron-phonon deformation potential for this particular mode. The value of Δμ/Δz=-(1.0-1.5) eV/Å is comparable with theoretical predictions and demonstrates the importance of this degree of freedom for the electron-phonon coupling in the Fe pnictides.
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Affiliation(s)
- L Rettig
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - S O Mariager
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - A Ferrer
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and Institute for Quantum Electronics, Physics Department, ETH Zürich, CH-8093 Zürich, Switzerland
| | - S Grübel
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - J A Johnson
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - J Rittmann
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide, ISIC, FSB, CH-1015 Lausanne, Switzerland
| | - T Wolf
- Karlsruhe Institute of Technology, Institut für Festkörperphysik, D-76021 Karlsruhe, Germany
| | - S L Johnson
- Institute for Quantum Electronics, Physics Department, ETH Zürich, CH-8093 Zürich, Switzerland
| | - G Ingold
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and SwissFEL, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - P Beaud
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and SwissFEL, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - U Staub
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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Charnukha A. Optical conductivity of iron-based superconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:253203. [PMID: 24899620 DOI: 10.1088/0953-8984/26/25/253203] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The new family of unconventional iron-based superconductors discovered in 2006 immediately relieved their copper-based high-temperature predecessors as the most actively studied superconducting compounds in the world. The experimental and theoretical effort made in order to unravel the mechanism of superconductivity in these materials has been overwhelming. Although our understanding of their microscopic properties has been improving steadily, the pairing mechanism giving rise to superconducting transition temperatures up to 55 K remains elusive. And yet the hope is strong that these materials, which possess a drastically different electronic structure but similarly high transition temperatures compared to the copper-based compounds, will shed essential new light onto the several-decade-old problem of unconventional superconductivity. In this work we review the current understanding of the itinerant-charge-carrier dynamics in the iron-based superconductors and parent compounds largely based on the optical conductivity data the community has gleaned over the past seven years using such experimental techniques as reflectivity, ellipsometry, and terahertz transmission measurements and analyze the implications of these studies for the microscopic properties of the iron-based materials as well as the mechanism of superconductivity therein.
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11
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Crystal-momentum dispersion of ultrafast spin change in fcc Co. Sci Rep 2014; 4:5010. [PMID: 24852331 PMCID: PMC4031477 DOI: 10.1038/srep05010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Accepted: 04/29/2014] [Indexed: 11/30/2022] Open
Abstract
Nearly twenty years ago, Beaurepaire and coworkers showed that when an ultrafast laser impinges on a ferromagnet, its spin moment undergoes a dramatic change, but how it works remains a mystery. While the current experiment is still unable to resolve the minute details of the spin change, crystal momentum-resolved techniques have long been used to analyze the charge dynamics in superconductors and strongly correlated materials. Here we extend it to probe spin moment change in the entire three-dimensional Brillouin zone for fcc Co. Our results indeed show a strong spin activity along the Δ line, supporting a prior experimental finding. The spin active pockets coalesce into a series of spin surfaces that follow the Fermi surfaces. We predict two largest spin change pockets which have been elusive to experiments: one pocket is slightly below the Δ line and the other is along the Λ line and close to the L point. Our theory presents an opportunity for the time-, spin- and momentum-resolve photoemission technique.
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Gotlieb K, Hussain Z, Bostwick A, Lanzara A, Jozwiak C. Rapid high-resolution spin- and angle-resolved photoemission spectroscopy with pulsed laser source and time-of-flight spectrometer. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:093904. [PMID: 24089838 DOI: 10.1063/1.4821247] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A high-efficiency spin- and angle-resolved photoemission spectroscopy (spin-ARPES) spectrometer is coupled with a laboratory-based laser for rapid high-resolution measurements. The spectrometer combines time-of-flight (TOF) energy measurements with low-energy exchange scattering spin polarimetry for high detection efficiencies. Samples are irradiated with fourth harmonic photons generated from a cavity-dumped Ti:sapphire laser that provides high photon flux in a narrow bandwidth, with a pulse timing structure ideally matched to the needs of the TOF spectrometer. The overall efficiency of the combined system results in near-E(F) spin-resolved ARPES measurements with an unprecedented combination of energy resolution and acquisition speed. This allows high-resolution spin measurements with a large number of data points spanning multiple dimensions of interest (energy, momentum, photon polarization, etc.) and thus enables experiments not otherwise possible. The system is demonstrated with spin-resolved energy and momentum mapping of the L-gap Au(111) surface states, a prototypical Rashba system. The successful integration of the spectrometer with the pulsed laser system demonstrates its potential for simultaneous spin- and time-resolved ARPES with pump-probe based measurements.
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Affiliation(s)
- K Gotlieb
- Graduate Group in Applied Science and Technology, University of California, Berkeley, California 94720, USA
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13
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Moritz B, Kemper AF, Sentef M, Devereaux TP, Freericks JK. Electron-mediated relaxation following ultrafast pumping of strongly correlated materials: model evidence of a correlation-tuned crossover between thermal and nonthermal states. PHYSICAL REVIEW LETTERS 2013; 111:077401. [PMID: 23992080 DOI: 10.1103/physrevlett.111.077401] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Indexed: 06/02/2023]
Abstract
We examine electron-electron mediated relaxation following ultrafast electric field pump excitation of the fermionic degrees of freedom in the Falicov-Kimball model for correlated electrons. The results reveal a dichotomy in the temporal evolution of the system as one tunes through the Mott metal-to-insulator transition: in the metallic regime relaxation can be characterized by evolution toward a steady state well described by Fermi-Dirac statistics with an increased effective temperature; however, in the insulating regime this quasithermal paradigm breaks down with relaxation toward a nonthermal state with a complicated electronic distribution as a function of momentum. We characterize the behavior by studying changes in the energy, photoemission response, and electronic distribution as functions of time. This relaxation may be observable qualitatively on short enough time scales that the electrons behave like an isolated system not in contact with additional degrees of freedom which would act as a thermal bath, especially when using strong driving fields and studying materials whose physics may manifest the effects of correlations.
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Affiliation(s)
- B Moritz
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
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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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Smallwood CL, Jozwiak C, Zhang W, Lanzara A. An ultrafast angle-resolved photoemission apparatus for measuring complex materials. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2012; 83:123904. [PMID: 23278002 DOI: 10.1063/1.4772070] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
We present technical specifications for a high resolution time- and angle-resolved photoemission spectroscopy setup based on a hemispherical electron analyzer and cavity-dumped solid state Ti:sapphire laser used to generate pump and probe beams, respectively, at 1.48 and 5.93 eV. The pulse repetition rate can be tuned from 209 Hz to 54.3 MHz. Under typical operating settings the system has an overall energy resolution of 23 meV, an overall momentum resolution of 0.003 Å(-1), and an overall time resolution of 310 fs. We illustrate the system capabilities with representative data on the cuprate superconductor Bi(2)Sr(2)CaCu(2)O(8+δ). The descriptions and analyses presented here will inform new developments in ultrafast electron spectroscopy.
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Smallwood CL, Hinton JP, Jozwiak C, Zhang W, Koralek JD, Eisaki H, Lee DH, Orenstein J, Lanzara A. Tracking Cooper Pairs in a Cuprate Superconductor by Ultrafast Angle-Resolved Photoemission. Science 2012; 336:1137-9. [DOI: 10.1126/science.1217423] [Citation(s) in RCA: 157] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Kim KW, Pashkin A, Schäfer H, Beyer M, Porer M, Wolf T, Bernhard C, Demsar J, Huber R, Leitenstorfer A. Ultrafast transient generation of spin-density-wave order in the normal state of BaFe2As2 driven by coherent lattice vibrations. NATURE MATERIALS 2012; 11:497-501. [PMID: 22484832 DOI: 10.1038/nmat3294] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Accepted: 03/05/2012] [Indexed: 05/31/2023]
Abstract
The interplay among charge, spin and lattice degrees of freedom in solids gives rise to intriguing macroscopic quantum phenomena such as colossal magnetoresistance, multiferroicity and high-temperature superconductivity. Strong coupling or competition between various orders in these systems presents the key to manipulate their functional properties by means of external perturbations such as electric and magnetic fields or pressure. Ultrashort and intense optical pulses have emerged as an interesting tool to investigate elementary dynamics and control material properties by melting an existing order. Here, we employ few-cycle multi-terahertz pulses to resonantly probe the evolution of the spin-density-wave (SDW) gap of the pnictide compound BaFe(2)As(2) following excitation with a femtosecond optical pulse. When starting in the low-temperature ground state, optical excitation results in a melting of the SDW order, followed by ultrafast recovery. In contrast, the SDW gap is induced when we excite the normal state above the transition temperature. Very surprisingly, the transient ordering quasi-adiabatically follows a coherent lattice oscillation at a frequency as high as 5.5 THz. Our results attest to a pronounced spin-phonon coupling in pnictides that supports rapid development of a macroscopic order on small vibrational displacement even without breaking the symmetry of the crystal.
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