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Wei Z, Qin S, Ding C, Wu X, Hu J, Sun YJ, Wang L, Xue QK. Identifying s-wave pairing symmetry in single-layer FeSe from topologically trivial edge states. Nat Commun 2023; 14:5302. [PMID: 37652936 PMCID: PMC10471577 DOI: 10.1038/s41467-023-40931-5] [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: 12/15/2022] [Accepted: 08/11/2023] [Indexed: 09/02/2023] Open
Abstract
Determining the pairing symmetry of single-layer FeSe on SrTiO3 is the key to understanding the enhanced pairing mechanism. It also guides the search for superconductors with high transition temperatures. Despite considerable efforts, it remains controversial whether the symmetry is the sign-preserving s- or the sign-changing s±-wave. Here, we investigate the pairing symmetry of single-layer FeSe from a topological point of view. Using low-temperature scanning tunneling microscopy/spectroscopy, we systematically characterize the superconducting states at edges and corners of single-layer FeSe. The tunneling spectra collected at edges and corners show a full energy gap and a substantial dip, respectively, suggesting the absence of topologically non-trivial edge and corner modes. According to our theoretical calculations, these spectroscopic features can be considered as strong evidence for the sign-preserving s-wave pairing in single-layer FeSe.
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Affiliation(s)
- Zhongxu Wei
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, China
| | - Shengshan Qin
- School of Physics, Beijing Institute of Technology, Beijing, 100081, China
- Kavli Institute of Theoretical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Cui Ding
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, China
- Beijing Academy of Quantum Information Sciences, Beijing, 100193, China
| | - Xianxin Wu
- CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Jiangping Hu
- Kavli Institute of Theoretical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100049, China
- Beijing National Research Center for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Yu-Jie Sun
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China.
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen, 518045, China.
| | - Lili Wang
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, China.
| | - Qi-Kun Xue
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China.
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, China.
- Beijing Academy of Quantum Information Sciences, Beijing, 100193, China.
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen, 518045, China.
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Li Y, Shen D, Kreisel A, Chen C, Wei T, Xu X, Wang J. Anisotropic Gap Structure and Sign Reversal Symmetry in Monolayer Fe(Se,Te). NANO LETTERS 2023; 23:140-147. [PMID: 36450010 DOI: 10.1021/acs.nanolett.2c03735] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
The iron-based superconductors are an ideal platform to reveal the enigma of the unconventional superconductivity and potential topological superconductivity. Among them, the monolayer Fe(Se,Te)/SrTiO3(001), which is proposed to be topological nontrivial, shows interface-enhanced high-temperature superconductivity in the two-dimensional limit. However, the experimental studies on the superconducting pairing mechanism of monolayer Fe(Se,Te) films are still limited. Here, by measuring the quasiparticle interference in monolayer Fe(Se,Te)/SrTiO3(001), we report the observation of the anisotropic structure of the large superconducting gap and the sign change of the superconducting gap on different electron pockets. The results are well consistent with the "bonding-antibonding" s±-wave pairing symmetry driven by spin fluctuations in conjunction with spin-orbit coupling. Our work is of basic significance not only for a unified superconducting formalism in the iron-based superconductors, but also for understanding of topological superconductivity in high-temperature superconductors.
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Affiliation(s)
- Yu Li
- International Center for Quantum Materials, School of Physics, Peking University, Beijing100871, China
| | - Dingyu Shen
- International Center for Quantum Materials, School of Physics, Peking University, Beijing100871, China
| | - Andreas Kreisel
- Institut für Theoretische Physik, Universität Leipzig, D-04103Leipzig, Germany
| | - Cheng Chen
- International Center for Quantum Materials, School of Physics, Peking University, Beijing100871, China
| | - Tianheng Wei
- International Center for Quantum Materials, School of Physics, Peking University, Beijing100871, China
| | - Xiaotong Xu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing100871, China
| | - Jian Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing100871, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing100190, China
- Beijing Academy of Quantum Information Sciences, Beijing100193, China
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Chakraborty D, Black-Schaffer AM. Quasiparticle Interference as a Direct Experimental Probe of Bulk Odd-Frequency Superconducting Pairing. PHYSICAL REVIEW LETTERS 2022; 129:247001. [PMID: 36563253 DOI: 10.1103/physrevlett.129.247001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Revised: 09/09/2022] [Accepted: 10/25/2022] [Indexed: 06/17/2023]
Abstract
We show that quasiparticle interference (QPI) due to omnipresent weak impurities and probed by Fourier transform scanning tunneling microscopy and spectroscopy acts as a direct experimental probe of bulk odd-frequency superconducting pairing. Taking the example of a conventional s-wave superconductor under applied magnetic field, we show that the nature of the QPI peaks can only be characterized by including the odd-frequency pairing correlations generated in this system. In particular, we identify that the defining feature of odd-frequency pairing gives rise to a bias asymmetry in the QPI, present generically in materials with odd-frequency pairing irrespective of its origin.
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Affiliation(s)
- Debmalya Chakraborty
- Department of Physics and Astronomy, Uppsala University, Box 516, S-751 20 Uppsala, Sweden
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Band Structure of Organic-Ion-Intercalated (EMIM) xFeSe Superconductor. MATERIALS 2022; 15:ma15051856. [PMID: 35269087 PMCID: PMC8911679 DOI: 10.3390/ma15051856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 02/17/2022] [Accepted: 02/25/2022] [Indexed: 12/10/2022]
Abstract
The band structure and the Fermi surface of the recently discovered superconductor (EMIM)xFeSe are studied within the density functional theory in the generalized gradient approximation. We show that the bands near the Fermi level are formed primarily by Fe-d orbitals. Although there is no direct contribution of EMIM orbitals to the near-Fermi level states, the presence of organic cations leads to a shift of the chemical potential. It results in the appearance of small electron pockets in the quasi-two-dimensional Fermi surface of (EMIM)xFeSe.
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Song SY, Martiny JHJ, Kreisel A, Andersen BM, Seo J. Visualization of Local Magnetic Moments Emerging from Impurities in Hund's Metal States of FeSe. PHYSICAL REVIEW LETTERS 2020; 124:117001. [PMID: 32242691 DOI: 10.1103/physrevlett.124.117001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 09/30/2019] [Accepted: 02/21/2020] [Indexed: 06/11/2023]
Abstract
Understanding the origin of the magnetism of high temperature superconductors is crucial for establishing their unconventional pairing mechanism. Recently, theory predicts that FeSe is close to a magnetic quantum critical point, and thus weak perturbations such as impurities could induce local magnetic moments. To elucidate such quantum instability, we have employed scanning tunneling microscopy and spectroscopy. In particular, we have grown FeSe film on superconducting Pb(111) using molecular beam epitaxy and investigated magnetic excitation caused by impurities in the proximity-induced superconducting gap of FeSe. Our study provides deep insight into the origin of the magnetic ordering of FeSe by showing the way local magnetic moments develop in response to impurities near the magnetic quantum critical point.
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Affiliation(s)
- Sang Yong Song
- Department of Emerging Materials Science, DGIST, 333 Techno-Jungang-daero, Hyeonpung-Eup, Dalseong-Gun, Daegu 42988, Korea
| | - J H J Martiny
- Center for Nanostructured Graphene (CNG), Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - A Kreisel
- Institut für Theoretische Physik, Universität Leipzig, D-04103 Leipzig, Germany
| | - B M Andersen
- Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, DK-2100 Copenhagen, Denmark
| | - Jungpil Seo
- Department of Emerging Materials Science, DGIST, 333 Techno-Jungang-daero, Hyeonpung-Eup, Dalseong-Gun, Daegu 42988, Korea
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