1
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Kim C, Bhoi D, Sur Y, Jeon BG, Wulferding D, Min BH, Kim J, Kim KH. Experimental signatures of nodeless multiband superconductivity in a [Formula: see text] single crystal. Sci Rep 2021; 11:13383. [PMID: 34183706 PMCID: PMC8239042 DOI: 10.1038/s41598-021-92709-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Accepted: 05/20/2021] [Indexed: 11/20/2022] Open
Abstract
In order to understand the superconducting gap nature of a [Formula: see text] single crystal with [Formula: see text], in-plane thermal conductivity [Formula: see text], in-plane London penetration depth [Formula: see text], and the upper critical fields [Formula: see text] have been investigated. At zero magnetic field, it is found that no residual linear term [Formula: see text] exists and [Formula: see text] follows a power-law [Formula: see text] (T: temperature) with n = 2.66 at [Formula: see text], supporting nodeless superconductivity. Moreover, the magnetic-field dependence of [Formula: see text]/T clearly shows a shoulder-like feature at a low field region. The temperature dependent [Formula: see text] curves for both in-plane and out-of-plane field directions exhibit clear upward curvatures near [Formula: see text], consistent with the shape predicted by the two-band theory and the anisotropy ratio between the [Formula: see text](T) curves exhibits strong temperature-dependence. All these results coherently suggest that [Formula: see text] is a nodeless, multiband superconductor.
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Affiliation(s)
- Chanhee Kim
- Department of Physics and Astronomy, Center for Novel States of Complex Materials Research, Seoul National University, Seoul, 08826 Republic of Korea
| | - Dilip Bhoi
- Department of Physics and Astronomy, Center for Novel States of Complex Materials Research, Seoul National University, Seoul, 08826 Republic of Korea
- Present Address: The Institute for Solid State Physics (ISSP), The Institute for solid state Physics, The University of Tokyo, Kashiwa, Chiba 277-8581 Japan
| | - Yeahan Sur
- Department of Physics and Astronomy, Center for Novel States of Complex Materials Research, Seoul National University, Seoul, 08826 Republic of Korea
| | - Byung-Gu Jeon
- Department of Physics and Astronomy, Center for Novel States of Complex Materials Research, Seoul National University, Seoul, 08826 Republic of Korea
| | - Dirk Wulferding
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang, 37673 South Korea
| | - Byeong Hun Min
- Department of Physics and Astronomy, Center for Novel States of Complex Materials Research, Seoul National University, Seoul, 08826 Republic of Korea
| | - Jeehoon Kim
- Department of Physics, Pohang University of Science and Technology, Pohang, 37673 South Korea
| | - Kee Hoon Kim
- Department of Physics and Astronomy, Center for Novel States of Complex Materials Research, Seoul National University, Seoul, 08826 Republic of Korea
- Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul, 08826 Republic of Korea
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2
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Abstract
Emergent electronic phenomena in iron-based superconductors have been at the forefront of condensed matter physics for more than a decade. Much has been learned about the origins and intertwined roles of ordered phases, including nematicity, magnetism, and superconductivity, in this fascinating class of materials. In recent years, focus has been centered on the peculiar and highly unusual properties of FeSe and its close cousins. This family of materials has attracted considerable attention due to the discovery of unexpected superconducting gap structures, a wide range of superconducting critical temperatures, and evidence for nontrivial band topology, including associated spin-helical surface states and vortex-induced Majorana bound states. Here, we review superconductivity in iron chalcogenide superconductors, including bulk FeSe, doped bulk FeSe, FeTe1−xSex, intercalated FeSe materials, and monolayer FeSe and FeTe1−xSex on SrTiO3. We focus on the superconducting properties, including a survey of the relevant experimental studies, and a discussion of the different proposed theoretical pairing scenarios. In the last part of the paper, we review the growing recent evidence for nontrivial topological effects in FeSe-related materials, focusing again on interesting implications for superconductivity.
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3
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Kasahara S, Sato Y, Licciardello S, Čulo M, Arsenijević S, Ottenbros T, Tominaga T, Böker J, Eremin I, Shibauchi T, Wosnitza J, Hussey NE, Matsuda Y. Evidence for an Fulde-Ferrell-Larkin-Ovchinnikov State with Segmented Vortices in the BCS-BEC-Crossover Superconductor FeSe. PHYSICAL REVIEW LETTERS 2020; 124:107001. [PMID: 32216412 DOI: 10.1103/physrevlett.124.107001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Accepted: 02/05/2020] [Indexed: 06/10/2023]
Abstract
We present resistivity and thermal-conductivity measurements of superconducting FeSe in intense magnetic fields up to 35 T applied parallel to the ab plane. At low temperatures, the upper critical field μ_{0}H_{c2}^{ab} shows an anomalous upturn, while thermal conductivity exhibits a discontinuous jump at μ_{0}H^{*}≈24 T well below μ_{0}H_{c2}^{ab}, indicating a first-order phase transition in the superconducting state. This demonstrates the emergence of a distinct field-induced superconducting phase. Moreover, the broad resistive transition at high temperatures abruptly becomes sharp upon entering the high-field phase, indicating a dramatic change of the magnetic-flux properties. We attribute the high-field phase to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state, where the formation of planar nodes gives rise to a segmentation of the flux-line lattice. We point out that strongly orbital-dependent pairing as well as spin-orbit interactions, the multiband nature, and the extremely small Fermi energy are important for the formation of the FFLO state in FeSe.
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Affiliation(s)
- S Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502 Japan
| | - Y Sato
- Department of Physics, Kyoto University, Kyoto 606-8502 Japan
| | - S Licciardello
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, 6525 ED Nijmegen, The Netherlands
| | - M Čulo
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, 6525 ED Nijmegen, The Netherlands
| | - S Arsenijević
- Hochfeld-Magnetlabor Dresden (HLD-EMFL) and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtz-Zentrum Dresden-Rossendorf, D-01328 Dresden, Germany
| | - T Ottenbros
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, 6525 ED Nijmegen, The Netherlands
| | - T Tominaga
- Department of Physics, Kyoto University, Kyoto 606-8502 Japan
| | - J Böker
- Institut für Theoretische Physik III, Ruhr-Universität Bochum, D-44801 Bochum, Germany
| | - I Eremin
- Institut für Theoretische Physik III, Ruhr-Universität Bochum, D-44801 Bochum, Germany
- National University of Science and Technology MISiS, 119049 Moscow, Russian Federation
| | - T Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Chiba 277-8561, Japan
| | - J Wosnitza
- Hochfeld-Magnetlabor Dresden (HLD-EMFL) and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtz-Zentrum Dresden-Rossendorf, D-01328 Dresden, Germany
- Institut für Festkörper- und Materialphysik, Technische Universität Dresden, 01062 Dresden, Germany
| | - N E Hussey
- High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, 6525 ED Nijmegen, The Netherlands
- H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, BS8 1TL, United Kingdom
| | - Y Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502 Japan
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4
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Chu J, Wang T, Ma Y, Feng J, Wang L, Xu X, Li W, Mu G, Xie X. Multiple gaps revealed by low temperature specific heat in the 1111-type CaFe 0.88Co 0.12AsF single crystals. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:455602. [PMID: 31341099 DOI: 10.1088/1361-648x/ab34b8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Low-temperature specific heat (SH) is measured on the 1111-type CaFe0.88 Co0.12AsF single crystals under different magnetic fields. A clear SH jump with the height [Formula: see text] mJ mol-1 K-2 is observed at the superconducting transition temperature T c . The electronic SH coefficient [Formula: see text] increases linearly with the field below 5 T and a kink is observed around 5 T, indicating a multi-gap feature in the present system. Such a sign is also reflected in the T c - B data. A detailed analysis shows that this behavior can be interpreted in terms of a two-gap scenario with the ratio [Formula: see text]-4.5.
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Affiliation(s)
- Jianan Chu
- 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. CAS Center for Excellence in Superconducting Electronics (CENSE), Shanghai 200050, People's Republic of China. University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
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5
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She JH, Lawler MJ, Kim EA. Quantum Spin Liquid Intertwining Nematic and Superconducting Order in Fese. PHYSICAL REVIEW LETTERS 2018; 121:237002. [PMID: 30576170 DOI: 10.1103/physrevlett.121.237002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 02/19/2018] [Indexed: 06/09/2023]
Abstract
Despite its seemingly simple composition and structure, the pairing mechanism of FeSe remains an open problem due to several striking phenomena. Among them are nematic order without magnetic order, nodeless gap and unusual inelastic neutron spectra with a broad continuum, and gap anisotropy consistent with orbital selection of unknown origin. Here we propose a microscopic description of a nematic quantum spin liquid that reproduces key features of neutron spectra. We then study how the spin fluctuations of the local moments lead to pairing within a spin-fermion model. We find the resulting superconducting order parameter to be nodeless s±d wave within each domain. Further we show that orbital dependent Kondo-like coupling can readily capture observed gap anisotropy. Our prediction calls for inelastic neutron scattering in a detwinned sample.
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Affiliation(s)
- Jian-Huang She
- Department of Physics, Cornell University, Ithaca, New York 14853, USA
| | - Michael J Lawler
- Department of Physics, Cornell University, Ithaca, New York 14853, USA
- Department of physics, Binghamton University, Vestal, New York 13850, USA
- Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, California 93106-4030, USA
| | - Eun-Ah Kim
- Department of Physics, Cornell University, Ithaca, New York 14853, USA
- Kavli Institute for Theoretical Physics, Kohn Hall, University of California, Santa Barbara, California 93106-4030, USA
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6
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Kang J, Fernandes RM, Chubukov A. Superconductivity in FeSe: The Role of Nematic Order. PHYSICAL REVIEW LETTERS 2018; 120:267001. [PMID: 30004771 DOI: 10.1103/physrevlett.120.267001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2018] [Indexed: 06/08/2023]
Abstract
Bulk FeSe is a special iron-based material in which superconductivity emerges inside a well-developed nematic phase. We present a microscopic model for this nematic superconducting state, which takes into account the mixing between s-wave and d-wave pairing channels and the changes in the orbital spectral weight promoted by the sign-changing nematic order parameter. We show that nematicity only weakly affects T_{c}, but gives rise to cos2θ variation of the pairing gap on the hole pocket, whose magnitude and size agrees with angle resolved photoemission spectroscopy and STM data. We further show that nematicity increases the weight of the d_{xz} orbital on the hole pocket, and increases (reduces) the weight of the d_{xy} orbital on the Y (X) electron pocket.
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Affiliation(s)
- Jian Kang
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32304, USA
| | - Rafael M Fernandes
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Andrey Chubukov
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
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7
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Sato Y, Kasahara S, Taniguchi T, Xing X, Kasahara Y, Tokiwa Y, Yamakawa Y, Kontani H, Shibauchi T, Matsuda Y. Abrupt change of the superconducting gap structure at the nematic critical point in FeSe 1-xS x. Proc Natl Acad Sci U S A 2018; 115:1227-1231. [PMID: 29363600 PMCID: PMC5819433 DOI: 10.1073/pnas.1717331115] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The emergence of the nematic electronic state that breaks rotational symmetry is one of the most fascinating properties of the iron-based superconductors, and has relevance to cuprates as well. FeSe has a unique ground state in which superconductivity coexists with a nematic order without long-range magnetic ordering, providing a significant opportunity to investigate the role of nematicity in the superconducting pairing interaction. Here, to reveal how the superconducting gap evolves with nematicity, we measure the thermal conductivity and specific heat of FeSe1 - x S x , in which the nematicity is suppressed by isoelectronic sulfur substitution and a nematic critical point (NCP) appears at [Formula: see text] We find that, in the whole nematic regime ([Formula: see text]), the field dependence of two quantities consistently shows two-gap behavior; one gap is small but highly anisotropic with deep minima or line nodes, and the other is larger and more isotropic. In stark contrast, in the tetragonal regime ([Formula: see text]), the larger gap becomes strongly anisotropic, demonstrating an abrupt change in the superconducting gap structure at the NCP. Near the NCP, charge fluctuations of [Formula: see text] and [Formula: see text] orbitals are enhanced equally in the tetragonal side, whereas they develop differently in the orthorhombic side. Our observation therefore directly implies that the orbital-dependent nature of the nematic fluctuations has a strong impact on the superconducting gap structure and hence on the pairing interaction.
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Affiliation(s)
- Yuki Sato
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | | | | | - Xiangzhuo Xing
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yuichi Kasahara
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
| | - Yoshifumi Tokiwa
- Center for Electronic Correlations and Magnetism, Institute of Physics, Augsburg University, 86159 Augsburg, Germany
| | - Youichi Yamakawa
- Department of Physics, Nagoya University, Nagoya 464-8602, Japan
| | - Hiroshi Kontani
- Department of Physics, Nagoya University, Nagoya 464-8602, Japan
| | - Takasada Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Chiba 277-8561, Japan
| | - Yuji Matsuda
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan;
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8
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Hashimoto T, Ota Y, Yamamoto HQ, Suzuki Y, Shimojima T, Watanabe S, Chen C, Kasahara S, Matsuda Y, Shibauchi T, Okazaki K, Shin S. Superconducting gap anisotropy sensitive to nematic domains in FeSe. Nat Commun 2018; 9:282. [PMID: 29348671 PMCID: PMC5773685 DOI: 10.1038/s41467-017-02739-y] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Accepted: 12/20/2017] [Indexed: 11/29/2022] Open
Abstract
The structure of the superconducting gap in unconventional superconductors holds a key to understand the momentum-dependent pairing interactions. In superconducting FeSe, there have been controversial results reporting nodal and nodeless gap structures, raising a fundamental issue of pairing mechanisms of iron-based superconductivity. Here, by utilizing polarization-dependent laser-excited angle-resolved photoemission spectroscopy, we report a detailed momentum dependence of the gap in single- and multi-domain regions of orthorhombic FeSe crystals. We confirm that the superconducting gap has a twofold in-plane anisotropy, associated with the nematicity due to orbital ordering. In twinned regions, we clearly find finite gap minima near the vertices of the major axis of the elliptical zone-centered Fermi surface, indicating a nodeless state. In contrast, the single-domain gap drops steeply to zero in a narrow angle range, evidencing for nascent nodes. Such unusual node lifting in multi-domain regions can be explained by the nematicity-induced time-reversal symmetry breaking near the twin boundaries. The superconducting gap structure of FeSe remains a debated issue. Here, Hashimoto et al. report momentum dependence of the gap in single- and multi-domain regions of orthorhombic FeSe crystals, revealing an unusual node lifting of the gap structure in multi-domain regions.
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Affiliation(s)
- Takahiro Hashimoto
- Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Yuichi Ota
- Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Haruyoshi Q Yamamoto
- Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Yuya Suzuki
- Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo, 113-8656, Japan
| | - Takahiro Shimojima
- Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo, 113-8656, Japan
| | - Shuntaro Watanabe
- Research Institute for Science and Technology, Tokyo University of Science, Chiba, 278-8510, Japan
| | - Chuangtian Chen
- Beijing Center for Crystal R&D, Chinese Academy of Science (CAS), Zhongguancun, Beijing, 100190, China
| | | | - Yuji Matsuda
- Department of Physics, Kyoto University, Kyoto, 606-8502, Japan
| | - Takasada Shibauchi
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba, 277-8561, Japan
| | - Kozo Okazaki
- Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba, 277-8581, Japan.
| | - Shik Shin
- Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba, 277-8581, Japan.
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9
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Böhmer AE, Kreisel A. Nematicity, magnetism and superconductivity in FeSe. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:023001. [PMID: 29240560 DOI: 10.1088/1361-648x/aa9caa] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.
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Affiliation(s)
- Anna E Böhmer
- Ames Laboratory, US DOE, Ames, IA 50011, United States of America
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10
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Sprau PO, Kostin A, Kreisel A, Böhmer AE, Taufour V, Canfield PC, Mukherjee S, Hirschfeld PJ, Andersen BM, Davis JCS. Discovery of orbital-selective Cooper pairing in FeSe. Science 2018; 357:75-80. [PMID: 28684522 DOI: 10.1126/science.aal1575] [Citation(s) in RCA: 236] [Impact Index Per Article: 39.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Accepted: 06/05/2017] [Indexed: 11/02/2022]
Abstract
The superconductor iron selenide (FeSe) is of intense interest owing to its unusual nonmagnetic nematic state and potential for high-temperature superconductivity. But its Cooper pairing mechanism has not been determined. We used Bogoliubov quasiparticle interference imaging to determine the Fermi surface geometry of the electronic bands surrounding the Γ = (0, 0) and X = (π/aFe, 0) points of FeSe and to measure the corresponding superconducting energy gaps. We show that both gaps are extremely anisotropic but nodeless and that they exhibit gap maxima oriented orthogonally in momentum space. Moreover, by implementing a novel technique, we demonstrate that these gaps have opposite sign with respect to each other. This complex gap configuration reveals the existence of orbital-selective Cooper pairing that, in FeSe, is based preferentially on electrons from the d yz orbitals of the iron atoms.
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Affiliation(s)
- P O Sprau
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853, USA.,Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - A Kostin
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853, USA.,Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - A Kreisel
- Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK 2100 Copenhagen, Denmark.,Institut für Theoretische Physik, Universität Leipzig, D-04103 Leipzig, Germany
| | - A E Böhmer
- Ames Laboratory, U.S. Department of Energy, Ames, IA 50011, USA
| | - V Taufour
- Ames Laboratory, U.S. Department of Energy, Ames, IA 50011, USA
| | - P C Canfield
- Ames Laboratory, U.S. Department of Energy, Ames, IA 50011, USA.,Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
| | - S Mukherjee
- Department of Physics, Binghamton University-State University of New York, Binghamton, NY, USA
| | - P J Hirschfeld
- Department of Physics, University of Florida, Gainesville, FL 32611, USA
| | - B M Andersen
- Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK 2100 Copenhagen, Denmark
| | - J C Séamus Davis
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853, USA. .,Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.,School of Physics and Astronomy, University of St Andrews, Fife KY16 9SS, Scotland.,Tyndall National Institute, University College Cork, Cork T12R5C, Ireland
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11
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Jiao L, Huang CL, Rößler S, Koz C, Rößler UK, Schwarz U, Wirth S. Superconducting gap structure of FeSe. Sci Rep 2017; 7:44024. [PMID: 28266654 PMCID: PMC5339780 DOI: 10.1038/srep44024] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Accepted: 02/01/2017] [Indexed: 11/26/2022] Open
Abstract
The microscopic mechanism governing the zero-resistance flow of current in some iron-based, high-temperature superconducting materials is not well understood up to now. A central issue concerning the investigation of these materials is their superconducting gap symmetry and structure. Here we present a combined study of low-temperature specific heat and scanning tunnelling microscopy measurements on single crystalline FeSe. The results reveal the existence of at least two superconducting gaps which can be represented by a phenomenological two-band model. The analysis of the specific heat suggests significant anisotropy in the gap magnitude with deep gap minima. The tunneling spectra display an overall "U"-shaped gap close to the Fermi level away as well as on top of twin boundaries. These results are compatible with the anisotropic nodeless models describing superconductivity in FeSe.
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Affiliation(s)
- Lin Jiao
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - Chien-Lung Huang
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - Sahana Rößler
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - Cevriye Koz
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | | | - Ulrich Schwarz
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
| | - Steffen Wirth
- Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany
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12
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Xu HC, Niu XH, Xu DF, Jiang J, Yao Q, Chen QY, Song Q, Abdel-Hafiez M, Chareev DA, Vasiliev AN, Wang QS, Wo HL, Zhao J, Peng R, Feng DL. Highly Anisotropic and Twofold Symmetric Superconducting Gap in Nematically Ordered FeSe_{0.93}S_{0.07}. PHYSICAL REVIEW LETTERS 2016; 117:157003. [PMID: 27768370 DOI: 10.1103/physrevlett.117.157003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2016] [Indexed: 06/06/2023]
Abstract
FeSe exhibits a novel ground state in which superconductivity coexists with a nematic order in the absence of any long-range magnetic order. Here, we report on an angle-resolved photoemission study on the superconducting gap structure in the nematic state of FeSe_{0.93}S_{0.07}, without the complications caused by Fermi surface reconstruction induced by magnetic order. We find that the superconducting gap shows a pronounced twofold anisotropy around the elliptical hole pocket near Z (0, 0, π), with gap minima at the end points of its major axis, while no detectable gap is observed around Γ (0, 0, 0) and the zone corner (π, π, k_{z}). The large anisotropy and nodal gap distribution demonstrate the substantial effects of the nematicity on the superconductivity and thus put strong constraints on current theories.
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Affiliation(s)
- H C Xu
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - X H Niu
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - D F Xu
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - J Jiang
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - Q Yao
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - Q Y Chen
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - Q Song
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - M Abdel-Hafiez
- Center for High Pressure Science and Technology Advanced Research, Beijing 100094, China
- Faculty of science, Physics Department, Fayoum University, 63514 Fayoum, Egypt
| | - D A Chareev
- Institute of Experimental Mineralogy, Russian Academy of Sciences, 142432 Chernogolovka, Moscow District, Russia
- Institute of Physics and Technology, Ural Federal University, 620002 Ekaterinburg, Russia
| | - A N Vasiliev
- Institute of Physics and Technology, Ural Federal University, 620002 Ekaterinburg, Russia
- Low Temperature Physics and Superconductivity Department, M.V. Lomonosov Moscow State University, 119991 Moscow, Russia
| | - Q S Wang
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - H L Wo
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - J Zhao
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - R Peng
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
| | - D L Feng
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, People's Republic of China
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