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Li H, Wang G, Ding N, Ren Q, Zhao G, Lin W, Yang J, Yan W, Li Q, Yang R, Yuan S, Denlinger JD, Wang Z, Zhang X, Wray LA, Dong S, Qian D, Miao L. Spectroscopic evidence of spin-state excitation in d-electron correlated semiconductor FeSb 2. Proc Natl Acad Sci U S A 2024; 121:e2321193121. [PMID: 38954549 PMCID: PMC11252798 DOI: 10.1073/pnas.2321193121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Accepted: 05/28/2024] [Indexed: 07/04/2024] Open
Abstract
Iron antimonide (FeSb2) has been investigated for decades due to its puzzling electronic properties. It undergoes the temperature-controlled transition from an insulator to an ill-defined metal, with a cross-over from diamagnetism to paramagnetism. Extensive efforts have been made to uncover the underlying mechanism, but a consensus has yet to be reached. While macroscopic transport and magnetic measurements can be explained by different theoretical proposals, the essential spectroscopic evidence required to distinguish the physical origin is missing. In this paper, through the use of X-ray absorption spectroscopy and atomic multiplet simulations, we have observed the mixed spin states of 3d 6 configuration in FeSb2. Furthermore, we reveal that the enhancement of the conductivity, whether induced by temperature or doping, is characterized by populating the high-spin state from the low-spin state. Our work constitutes vital spectroscopic evidence that the electrical/magnetical transition in FeSb2 is directly associated with the spin-state excitation.
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Affiliation(s)
- Huayao Li
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
| | - Guohua Wang
- School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai200240, China
| | - Ning Ding
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
| | - Quan Ren
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
| | - Gan Zhao
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
| | - Wenting Lin
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
| | - Jinchuan Yang
- School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai200240, China
| | - Wensheng Yan
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei230029, China
| | - Qian Li
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei230029, China
| | - Run Yang
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
| | - Shijun Yuan
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
| | | | - Zhenxing Wang
- Wuhan National High Magnetic Field Center & School of Physics, Huazhong University of Science and Technology, Wuhan430074, China
| | - Xiaoqian Zhang
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
| | - L. Andrew Wray
- Department of Physics, New York University, New York, NY10003
| | - Shuai Dong
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
| | - Dong Qian
- School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai200240, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing210093, China
- Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai200240, China
| | - Lin Miao
- Key Laboratory of Quantum Materials and Devices of Ministry of Education, School of Physics, Southeast University, Nanjing211189, China
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Breindel AJ, Deng Y, Moir CM, Fang Y, Ran S, Lou H, Li S, Zeng Q, Shu L, Wolowiec CT, Schuller IK, Rosa PFS, Fisk Z, Singleton J, Maple MB. Probing FeSi, a d-electron topological Kondo insulator candidate, with magnetic field, pressure, and microwaves. Proc Natl Acad Sci U S A 2023; 120:e2216367120. [PMID: 36791111 PMCID: PMC9974408 DOI: 10.1073/pnas.2216367120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Accepted: 01/12/2023] [Indexed: 02/16/2023] Open
Abstract
Recently, evidence for a conducting surface state (CSS) below 19 K was reported for the correlated d-electron small gap semiconductor FeSi. In the work reported herein, the CSS and the bulk phase of FeSi were probed via electrical resistivity ρ measurements as a function of temperature T, magnetic field B to 60 T, and pressure P to 7.6 GPa, and by means of a magnetic field-modulated microwave spectroscopy (MFMMS) technique. The properties of FeSi were also compared with those of the Kondo insulator SmB6 to address the question of whether FeSi is a d-electron analogue of an f-electron Kondo insulator and, in addition, a "topological Kondo insulator" (TKI). The overall behavior of the magnetoresistance of FeSi at temperatures above and below the onset temperature TS = 19 K of the CSS is similar to that of SmB6. The two energy gaps, inferred from the ρ(T) data in the semiconducting regime, increase with pressure up to about 7 GPa, followed by a drop which coincides with a sharp suppression of TS. Several studies of ρ(T) under pressure on SmB6 reveal behavior similar to that of FeSi in which the two energy gaps vanish at a critical pressure near the pressure at which TS vanishes, although the energy gaps in SmB6 initially decrease with pressure, whereas in FeSi they increase with pressure. The MFMMS measurements showed a sharp feature at TS ≈ 19 K for FeSi, which could be due to ferromagnetic ordering of the CSS. However, no such feature was observed at TS ≈ 4.5 K for SmB6.
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Affiliation(s)
| | - Yuhang Deng
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | - Camilla M. Moir
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | - Yuankan Fang
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | - Sheng Ran
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | - Hongbo Lou
- Center for High Pressure Science and Technology Advanced Research, Pudong, Shanghai201203, People’s Republic of China
| | - Shubin Li
- Center for High Pressure Science and Technology Advanced Research, Pudong, Shanghai201203, People’s Republic of China
- Univ Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, Villeurbanne69100, France
| | - Qiaoshi Zeng
- Center for High Pressure Science and Technology Advanced Research, Pudong, Shanghai201203, People’s Republic of China
| | - Lei Shu
- State Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai200433, People’s Republic of China
- Shanghai Research Center for Quantum Sciences, Shanghai201315, People’s Republic of China
| | | | - Ivan K. Schuller
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
| | | | - Zachary Fisk
- University of California Irvine, Irvine, CA92967
| | | | - M. Brian Maple
- Department of Physics, University of CaliforniaSan Diego, La Jolla, CA92093
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Lima ACP, Ribeiro RCB, Correa JH, Deus F, Figueira MS, Continentino MA. Thermoelectric properties of topological chains coupled to a quantum dot. Sci Rep 2023; 13:1508. [PMID: 36707603 PMCID: PMC9883525 DOI: 10.1038/s41598-023-28491-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Accepted: 01/19/2023] [Indexed: 01/28/2023] Open
Abstract
Topological one-dimensional superconductors can sustain zero energy modes protected by different kinds of symmetries in their extremities. Observing these excitations in the form of Majorana fermions is one of the most intensive quests in condensed matter physics. We are interested in another class of one-dimensional topological systems in this work, namely topological insulators. Which present symmetry-protected end modes with robust properties and do not require the low temperatures necessary for topological superconductivity. We consider a device in the form of a single electron transistor coupled to the simplest kind of topological insulators, namely chains of atoms with hybridized sp orbitals. We study the thermoelectric properties of the device in the trivial, non-trivial topological phases and at the quantum topological transition of the chains. We show that the device's electrical conductance and the Wiedemann-Franz ratio at the topological transition have universal values at very low temperatures. The conductance and thermopower of the device with diatomic sp-chains, at their topological transition, give direct evidence of fractional charges in the system. The former has an anomalous low-temperature behavior, attaining a universal value that is a consequence of the double degeneracy of the system due to the presence of zero energy modes. On the other hand, the system can be tuned to exhibit high values of the thermoelectric figure of merit and the power factor at high temperatures.
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Affiliation(s)
- A. C. P. Lima
- grid.418228.50000 0004 0643 8134Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, Urca, Rio de Janeiro, RJ 22290-180 Brazil
| | - R. C. Bento Ribeiro
- grid.418228.50000 0004 0643 8134Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, Urca, Rio de Janeiro, RJ 22290-180 Brazil
| | - J. H. Correa
- grid.441911.80000 0001 1818 386XUniversidad Tecnológica Del Perú, Nathalio Sanchez, 125, 15046 Lima, Peru
| | - Fernanda Deus
- grid.412211.50000 0004 4687 5267Universidade do Estado do Rio de Janeiro, Rodovia Presidente Dutra km 298, Resende, RJ 27537-000 Brazil
| | - M. S. Figueira
- grid.411173.10000 0001 2184 6919Instituto de Física, Universidade Federal Fluminense, Av. Litorânea s/N, Niterói, RJ 24210-340 Brazil
| | - Mucio A. Continentino
- grid.418228.50000 0004 0643 8134Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, Urca, Rio de Janeiro, RJ 22290-180 Brazil
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Prediction of unconventional magnetism in doped FeSb 2. Proc Natl Acad Sci U S A 2021; 118:2108924118. [PMID: 34649995 DOI: 10.1073/pnas.2108924118] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/02/2021] [Indexed: 11/18/2022] Open
Abstract
It is commonly believed that the energy bands of typical collinear antiferromagnets (AFs), which have zero net magnetization, are Kramers spin-degenerate. Kramers nondegeneracy is usually associated with a global time-reversal symmetry breaking (e.g., via ferromagnetism) or with a combination of spin-orbit interaction and broken spatial inversion symmetry. Recently, another type of spin splitting was demonstrated to emerge in some collinear magnets that are fully spin compensated by symmetry, nonrelativistic, and not even necessarily noncentrosymmetric. These materials feature nonzero spin density staggered in real space as seen in traditional AFs but also spin splitting in momentum space, generally seen only in ferromagnets. This results in a combination of materials characteristics typical of both ferromagnets and AFs. Here, we discuss this recently discovered class with application to a well-known semiconductor, FeSb2, and predict that with certain alloying, it becomes magnetic and metallic and features the aforementioned magnetic dualism. The calculated energy bands split antisymmetrically with respect to spin-degenerate nodal surfaces rather than nodal points, as in the case of spin-orbit splitting. The combination of a large (0.2-eV) spin splitting, compensated net magnetization with metallic ground state, and a specific magnetic easy axis generates a large anomalous Hall conductivity (∼150 S/cm) and a sizable magnetooptical Kerr effect, all deemed to be hallmarks of nonzero net magnetization. We identify a large contribution to the anomalous response originating from the spin-orbit interaction gapped anti-Kramers nodal surfaces, a mechanism distinct from the nodal lines and Weyl points in ferromagnets.
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Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb 2. Proc Natl Acad Sci U S A 2020; 117:15409-15413. [PMID: 32571928 DOI: 10.1073/pnas.2002361117] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The resistance of a conventional insulator diverges as temperature approaches zero. The peculiar low-temperature resistivity saturation in the 4f Kondo insulator (KI) SmB6 has spurred proposals of a correlation-driven topological Kondo insulator (TKI) with exotic ground states. However, the scarcity of model TKI material families leaves difficulties in disentangling key ingredients from irrelevant details. Here we use angle-resolved photoemission spectroscopy (ARPES) to study FeSb2, a correlated d-electron KI candidate that also exhibits a low-temperature resistivity saturation. On the (010) surface, we find a rich assemblage of metallic states with two-dimensional dispersion. Measurements of the bulk band structure reveal band renormalization, a large temperature-dependent band shift, and flat spectral features along certain high-symmetry directions, providing spectroscopic evidence for strong correlations. Our observations suggest that exotic insulating states resembling those in SmB6 and YbB12 may also exist in systems with d instead of f electrons.
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