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Liu YP, Zhang YJ, Dong JJ, Lee H, Wei ZX, Zhang WL, Chen CY, Yuan HQ, Yang YF, Qi J. Hybridization Dynamics in CeCoIn_{5} Revealed by Ultrafast Optical Spectroscopy. PHYSICAL REVIEW LETTERS 2020; 124:057404. [PMID: 32083911 DOI: 10.1103/physrevlett.124.057404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 01/14/2020] [Accepted: 01/15/2020] [Indexed: 06/10/2023]
Abstract
We investigate the quasiparticle dynamics in the prototypical heavy fermion CeCoIn_{5} using ultrafast optical pump-probe spectroscopy. Our results indicate that this material system undergoes hybridization fluctuations before the establishment of heavy electron coherence, as the temperature decreases from ∼120 K (T^{†}) to ∼55 K (T^{*}). We reveal that the anomalous coherent phonon softening and damping reduction below T^{*} are directly associated with the emergence of collective hybridization. We also discover a distinct collective mode with an energy of ∼8 meV, which may be experimental evidence of the predicted unconventional density wave. Our findings provide important information for understanding the hybridization dynamics in heavy fermion systems.
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Affiliation(s)
- Y P Liu
- State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 611731, China
- Institute of Modern Physics, Fudan University, Shanghai 200433, China
| | - Y J Zhang
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - J J Dong
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Science, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - H Lee
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Z X Wei
- State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 611731, China
- Institute of Electronic and Information Engineering, University of Electronic Science and Technology of China, Dongguan 523808, China
| | - W L Zhang
- State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 611731, China
| | - C Y Chen
- Institute of Modern Physics, Fudan University, Shanghai 200433, China
| | - H Q Yuan
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, China
| | - Yi-Feng Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Science, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan 523808, China
| | - J Qi
- State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 611731, China
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2
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Yang JW, An L. Structure, elastic characteristic, ideal strengths, and phonon stability of binary uranium intermetallic UGe 3 of AuCu 3-type. Phys Chem Chem Phys 2020; 22:1381-1391. [PMID: 31858101 DOI: 10.1039/c9cp04971a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Crystallographic characterization, energy band structure, densities of states and charge density, elastic properties, ideal tensile and shear strengths, lattice dynamics and thermophysical characteristics of UGe3 of AuCu3-type have been studied by employing the first principles method based on Density Functional Theory (DFT). The optimized lattice parameters, such as lattice constant a, equilibrium cell volume V0, U-Ge distance and U-U distance of UGe3, are in favorable agreement with the available experimental results. Three single-crystalline elastic constants of C11, C12, and C44 have been obtained using the "energy-strain" technique by increasingly varying small strains. The polycrystalline elastic moduli including volume modulus B, Young's modulus E, and shear modulus G, Poisson's ratio v, brittle/ductile nature, Debye temperature θD, and the integration of elastic wave velocities over different crystallographic directions have also been successfully calculated. The anisotropy of the three-directional bulk modulus and Young's modulus is systematically explored and analyzed. The calculations indicate that UGe3 of AuCu3-type should be stabilized mechanically, and the system possesses insignificant elastic anisotropy. In particular, the vibrational spectrum, phonon densities of states and the infrared-active and inactive vibration modes at the center of the Brillouin zone are determined using Density Functional Perturbation Theory (DFPT) and group theory for the first time. This study reveals that UGe3 of AuCu3-type is also stable dynamically. Finally, within the calculated phonon densities of states and the quasi-harmonic Debye model, the constant volume heat capacity Cv and the vibration entropy S in the temperature range of 0-1000 K are predicted and analyzed comprehensively. The present investigations are expected to provide some valuable references for further exploring the properties of uranium compounds.
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Affiliation(s)
- Jin-Wen Yang
- Department of Physics, Taiyuan Normal University, Jinzhong 030619, China.
| | - Li An
- Department of Physics, Taiyuan Normal University, Jinzhong 030619, China.
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3
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Giannakis I, Leshen J, Kavai M, Ran S, Kang CJ, Saha SR, Zhao Y, Xu Z, Lynn JW, Miao L, Wray LA, Kotliar G, Butch NP, Aynajian P. Orbital-selective Kondo lattice and enigmatic f electrons emerging from inside the antiferromagnetic phase of a heavy fermion. SCIENCE ADVANCES 2019; 5:eaaw9061. [PMID: 31667341 PMCID: PMC6799987 DOI: 10.1126/sciadv.aaw9061] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 09/25/2019] [Indexed: 05/25/2023]
Abstract
Novel electronic phenomena frequently form in heavy-fermions because of the mutual localized and itinerant nature of f-electrons. On the magnetically ordered side of the heavy-fermion phase diagram, f-moments are expected to be localized and decoupled from the Fermi surface. It remains ambiguous whether Kondo lattice can develop inside the magnetically ordered phase. Using spectroscopic imaging with scanning tunneling microscope, complemented by neutron scattering, x-ray absorption spectroscopy, and dynamical mean field theory, we probe the electronic states in antiferromagnetic USb2. We visualize a large gap in the antiferromagnetic phase within which Kondo hybridization develops below ~80 K. Our calculations indicate the antiferromagnetism and Kondo lattice to reside predominantly on different f-orbitals, promoting orbital selectivity as a new conception into how these phenomena coexist in heavy-fermions. Finally, at 45 K, we find a novel first order-like transition through abrupt emergence of nontrivial 5f-electronic states that may resemble the "hidden-order" phase of URu2Si2.
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Affiliation(s)
- Ioannis Giannakis
- Department of Physics, Applied Physics, and Astronomy, Binghamton University, Binghamton, NY 13902, USA
| | - Justin Leshen
- Department of Physics, Applied Physics, and Astronomy, Binghamton University, Binghamton, NY 13902, USA
| | - Mariam Kavai
- Department of Physics, Applied Physics, and Astronomy, Binghamton University, Binghamton, NY 13902, USA
| | - Sheng Ran
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Chang-Jong Kang
- Department of Physics and Astronomy, Rutgers University, NJ 08854, USA
| | - Shanta R. Saha
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Y. Zhao
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA
| | - Z. Xu
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - J. W. Lynn
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Lin Miao
- Department of Physics, New York University, New York, NY 10003, USA
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - L. Andrew Wray
- Department of Physics, New York University, New York, NY 10003, USA
| | - Gabriel Kotliar
- Department of Physics and Astronomy, Rutgers University, NJ 08854, USA
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Nicholas P. Butch
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
- Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Pegor Aynajian
- Department of Physics, Applied Physics, and Astronomy, Binghamton University, Binghamton, NY 13902, USA
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4
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Miao L, Basak R, Ran S, Xu Y, Kotta E, He H, Denlinger JD, Chuang YD, Zhao Y, Xu Z, Lynn JW, Jeffries JR, Saha SR, Giannakis I, Aynajian P, Kang CJ, Wang Y, Kotliar G, Butch NP, Wray LA. High temperature singlet-based magnetism from Hund's rule correlations. Nat Commun 2019; 10:644. [PMID: 30733441 PMCID: PMC6367396 DOI: 10.1038/s41467-019-08497-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Accepted: 01/10/2019] [Indexed: 11/24/2022] Open
Abstract
Uranium compounds can manifest a wide range of fascinating many-body phenomena, and are often thought to be poised at a crossover between localized and itinerant regimes for 5f electrons. The antiferromagnetic dipnictide USb2 has been of recent interest due to the discovery of rich proximate phase diagrams and unusual quantum coherence phenomena. Here, linear-dichroic X-ray absorption and elastic neutron scattering are used to characterize electronic symmetries on uranium in USb2 and isostructural UBi2. Of these two materials, only USb2 is found to enable strong Hund’s rule alignment of local magnetic degrees of freedom, and to undergo distinctive changes in local atomic multiplet symmetry across the magnetic phase transition. Theoretical analysis reveals that these and other anomalous properties of the material may be understood by attributing it as the first known high temperature realization of a singlet ground state magnet, in which magnetism occurs through a process that resembles exciton condensation. Electrons in uranium-based materials are often on the border between localised and itinerant behaviour, which can lead to unusual magnetic behaviour. Here the authors combine experiment and theory to show that USb2 may be an unusually high temperature example of a singlet-ground-state magnet.
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Affiliation(s)
- Lin Miao
- Department of Physics, New York University, New York, NY, 10003, USA.,Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Rourav Basak
- Department of Physics, New York University, New York, NY, 10003, USA
| | - Sheng Ran
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - Yishuai Xu
- Department of Physics, New York University, New York, NY, 10003, USA
| | - Erica Kotta
- Department of Physics, New York University, New York, NY, 10003, USA
| | - Haowei He
- Department of Physics, New York University, New York, NY, 10003, USA
| | - Jonathan D Denlinger
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Yi-De Chuang
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Y Zhao
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA.,Department of Materials Science and Engineering, University of Maryland, College Park, MD, 20742, USA
| | - Z Xu
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - J W Lynn
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - J R Jeffries
- Materials Science Division, Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA
| | - S R Saha
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA.,Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, MD, 20742, USA
| | - Ioannis Giannakis
- Department of Physics, Applied Physics and Astronomy, Binghamton University, Binghamton, NY, 13902, USA
| | - Pegor Aynajian
- Department of Physics, Applied Physics and Astronomy, Binghamton University, Binghamton, NY, 13902, USA
| | - Chang-Jong Kang
- Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, 08854-8019, USA
| | - Yilin Wang
- Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY, 11973, USA
| | - Gabriel Kotliar
- Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, 08854-8019, USA
| | - Nicholas P Butch
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA.,Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, MD, 20742, USA
| | - L Andrew Wray
- Department of Physics, New York University, New York, NY, 10003, USA.
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5
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Chen RY, Zhang SJ, Zhang MY, Dong T, Wang NL. Revealing Extremely Low Energy Amplitude Modes in the Charge-Density-Wave Compound LaAgSb_{2}. PHYSICAL REVIEW LETTERS 2017; 118:107402. [PMID: 28339262 DOI: 10.1103/physrevlett.118.107402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Indexed: 06/06/2023]
Abstract
Using infrared spectroscopy and ultrafast pump probe measurement, we have studied the two charge-density-wave (CDW) instabilities in the layered compound LaAgSb_{2}. The development of CDW energy gaps was clearly observed by optical spectroscopy, which removed most of the free carrier spectral weight. More interestingly, our time-resolved measurements revealed two coherent oscillations that softened by approaching the two phase transition temperatures, respectively. We addressed that these two oscillations come from the amplitude modes of CDW collective excitations, the surprisingly low energies (0.12 THz and 0.34 THz for the higher and lower temperature ones, respectively) of which are associated with the extremely small nesting wave vectors. Additionally, the amplitude and relaxation time of photoinduced reflectivity of LaAgSb_{2} single crystals stayed unchanged across the CDW phase transitions, which is quite rare and deserves further investigation.
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Affiliation(s)
- R Y Chen
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing 100875, China
| | - S J Zhang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - M Y Zhang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - T Dong
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - N L Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
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6
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Fujimori SI. Band structures of 4f and 5f materials studied by angle-resolved photoelectron spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:153002. [PMID: 26974712 DOI: 10.1088/0953-8984/28/15/153002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Recent remarkable progress in angle-resolved photoelectron spectroscopy (ARPES) has enabled the direct observation of the band structures of 4f and 5f materials. In particular, ARPES with various light sources such as lasers (hν ~ 7 eV) or high-energy synchrotron radiations (hν >/~ 400 eV) has shed light on the bulk band structures of strongly correlated materials with energy scales of a few millielectronvolts to several electronvolts. The purpose of this paper is to summarize the behaviors of 4f and 5f band structures of various rare-earth and actinide materials observed by modern ARPES techniques, and understand how they can be described using various theoretical frameworks. For 4f-electron materials, ARPES studies of CeMIn5(M = Rh, Ir, and Co) and YbRh2Si2 with various incident photon energies are summarized. We demonstrate that their 4f electronic structures are essentially described within the framework of the periodic Anderson model, and that the band-structure calculation based on the local density approximation cannot explain their low-energy electronic structures. Meanwhile, electronic structures of 5f materials exhibit wide varieties ranging from itinerant to localized states. For itinerant U5f compounds such as UFeGa5, their electronic structures can be well-described by the band-structure calculation assuming that all U5f electrons are itinerant. In contrast, the band structures of localized U5f compounds such as UPd3 and UO2 are essentially explained by the localized model that treats U5f electrons as localized core states. In regards to heavy fermion U-based compounds such as the hidden-order compound URu2Si2, their electronic structures exhibit complex behaviors. Their overall band structures are generally well-explained by the band-structure calculation, whereas the states in the vicinity of EF show some deviations due to electron correlation effects. Furthermore, the electronic structures of URu2Si2 in the paramagnetic and hidden-order phases are summarized based on various ARPES studies. The present status of the field as well as possible future directions are also discussed.
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Affiliation(s)
- Shin-ichi Fujimori
- Condensed Matter Science Division, Japan Atomic Energy Agency, Hyogo 679-5148, Japan
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7
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Wang MC, Qiao S, Jiang Z, Luo SN, Qi J. Unraveling Photoinduced Spin Dynamics in the Topological Insulator Bi(2)Se(3). PHYSICAL REVIEW LETTERS 2016; 116:036601. [PMID: 26849605 DOI: 10.1103/physrevlett.116.036601] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2015] [Indexed: 06/05/2023]
Abstract
We report on a time-resolved ultrafast optical spectroscopy study of the topological insulator Bi_{2}Se_{3}. We unravel that a net spin polarization cannot only be generated using circularly polarized light via interband transitions between topological surface states (SSs), but also via transitions between SSs and bulk states. Our experiment demonstrates that tuning photon energy or temperature can essentially allow for photoexcitation of spin-polarized electrons to unoccupied topological SSs with two distinct spin relaxation times (∼25 and ∼300 fs), depending on the coupling between SSs and bulk states. The intrinsic mechanism leading to such distinctive spin dynamics is the scattering in SSs and bulk states which is dominated by E_{g}^{2} and A_{1g}^{1} phonon modes, respectively. These findings are suggestive of novel ways to manipulate the photoinduced coherent spins in topological insulators.
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Affiliation(s)
- M C Wang
- The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031, People's Republic of China
- Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, Sichuan 610031, People's Republic of China
| | - S Qiao
- State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, People's Republic of China
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 200031, People's Republic of China
| | - Z Jiang
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | - S N Luo
- The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031, People's Republic of China
- Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, Sichuan 610031, People's Republic of China
| | - J Qi
- The Peac Institute of Multiscale Sciences, Chengdu, Sichuan 610031, People's Republic of China
- Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, Sichuan 610031, People's Republic of China
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8
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Zhang GP, Gu M, Wu XS. Ultrafast reduction in exchange interaction by a laser pulse: alternative path to femtomagnetism. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:376001. [PMID: 25156910 DOI: 10.1088/0953-8984/26/37/376001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Since the beginning of femtomagnetism, it has been hotly debated how an ultrafast laser pulse can demagnetize a sample and switch its spins within a few hundred femtoseconds, but no consensus has been reached. In this paper, we propose that an ultrafast reduction in the exchange interaction by a femtosecond laser pulse is mainly responsible for demagnetization and spin switching. The key physics is that the dipole selection rule demands two distinctive electron configurations for the ground and excited states and consequently changes the exchange interaction. Although the exchange interaction change is almost instantaneous, its effect on the spin is delayed by the finite spin wave propagation. Consistent with the experimental observation, the delay becomes longer with a stronger exchange interaction pulse. In spin-frustrated systems, the effect of the exchange interaction change is even more dramatic, where the spin can be directly switched from one direction to the other. Therefore, our theory has the potential to explain the essence of major observations in rare-earth transition metal compounds for the last seven years. Our findings are likely to motivate further research in the quest of the origin of femtomagnetism.
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Affiliation(s)
- G P Zhang
- Department of Physics, Indiana State University, Terre Haute, IN 47809, USA
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9
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Gofryk K, Saparov B, Durakiewicz T, Chikina A, Danzenbächer S, Vyalikh DV, Graf MJ, Sefat AS. Fermi-surface reconstruction and complex phase equilibria in CaFe2As2. PHYSICAL REVIEW LETTERS 2014; 112:186401. [PMID: 24856707 DOI: 10.1103/physrevlett.112.186401] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Indexed: 06/03/2023]
Abstract
Fermi-surface topology governs the relationship between magnetism and superconductivity in iron-based materials. Using low-temperature transport, angle-resolved photoemission, and x-ray diffraction, we show unambiguous evidence of large Fermi-surface reconstruction in CaFe2As2 at magnetic spin-density-wave and nonmagnetic collapsed-tetragonal (cT) transitions. For the cT transition, the change in the Fermi-surface topology has a different character with no contribution from the hole part of the Fermi surface. In addition, the results suggest that the pressure effect in CaFe2As2 is mainly leading to a rigid-band-like change of the valence electronic structure. We discuss these results and their implications for magnetism and superconductivity in this material.
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Affiliation(s)
- K Gofryk
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - B Saparov
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - T Durakiewicz
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - A Chikina
- Department of Physics, St. Petersburg State University, St. Petersburg 198504, Russia and Institute of Solid State Physics, Dresden University of Technology, Zellescher Weg 16, D-01062 Dresden, Germany
| | - S Danzenbächer
- Institute of Solid State Physics, Dresden University of Technology, Zellescher Weg 16, D-01062 Dresden, Germany
| | - D V Vyalikh
- Department of Physics, St. Petersburg State University, St. Petersburg 198504, Russia and Institute of Solid State Physics, Dresden University of Technology, Zellescher Weg 16, D-01062 Dresden, Germany
| | - M J Graf
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - A S Sefat
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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