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Li Y, Zhao Y, Wang X, Liu W, He J, Luo X, Liu J, Liu Y. Precise Construction and Growth of Submillimeter Two-Dimensional WSe 2 and MoSe 2 Monolayers. Materials (Basel) 2023; 16:4795. [PMID: 37445110 DOI: 10.3390/ma16134795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Revised: 06/26/2023] [Accepted: 07/01/2023] [Indexed: 07/15/2023]
Abstract
Currently, as shown by large-scale research on two-dimensional materials in the field of nanoelectronics and catalysis, the construction of large-area two-dimensional materials is crucial for the development of devices and their application in photovoltaics, sensing, optoelectronics, and energy generation/storage. Here, using atmospheric-pressure chemical vapor deposition, we developed a method to regulate growth conditions according to the growth mechanism for WSe2 and MoSe2 materials. By accurately controlling the hydrogen flux within the range of 1 sccm and the distance between the precursor and the substrate, we obtained large-size films of single atomic layers with thicknesses of only about 1 nm. When growing the samples, we could not only obtain a 100 percent proportion of samples with the same shape, but the samples could also be glued into pieces of 700 μm and above in size, changing the shape and making it possible to reach the millimeter/submillimeter level visible to the naked eye. Our method is an effective method for the growth of large-area films with universal applicability.
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Affiliation(s)
- Yuqing Li
- International School of Materials Science and Engineering (ISMSE), State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
| | - Yuyan Zhao
- Southwest Institute of Technical Physics, Chengdu 610041, China
| | - Xiaoqian Wang
- International School of Materials Science and Engineering (ISMSE), State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
| | - Wanli Liu
- International School of Materials Science and Engineering (ISMSE), State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
| | - Jiazhen He
- International School of Materials Science and Engineering (ISMSE), State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
| | - Xuemin Luo
- International School of Materials Science and Engineering (ISMSE), State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
| | - Jinfeng Liu
- International School of Materials Science and Engineering (ISMSE), State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
| | - Yong Liu
- International School of Materials Science and Engineering (ISMSE), State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China
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2
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Abstract
The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.
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Affiliation(s)
- Anupam Giri
- Department of Chemistry, Faculty of Science, University of Allahabad, Prayagraj, UP-211002, India
| | - Gyeongbae Park
- Department of Materials Science and Engineering, Pohang University of Science and Technology, Cheongam-Ro 77, Nam-Gu, Pohang, Gyeongbuk790-784, Korea.,Functional Materials and Components R&D Group, Korea Institute of Industrial Technology, Gwahakdanji-ro 137-41, Sacheon-myeon, Gangneung, Gangwon-do25440, Republic of Korea
| | - Unyong Jeong
- Department of Materials Science and Engineering, Pohang University of Science and Technology, Cheongam-Ro 77, Nam-Gu, Pohang, Gyeongbuk790-784, Korea
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3
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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 Lett 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] [What about the content of this article? (0)] [Affiliation(s)] [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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4
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Yue C, Nomura Y, Werner P. Doping Asymmetry and Layer-Selective Metal-Insulator Transition in Trilayer K_{3+x}C_{60}. Phys Rev Lett 2022; 129:066403. [PMID: 36018629 DOI: 10.1103/physrevlett.129.066403] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2021] [Accepted: 07/18/2022] [Indexed: 06/15/2023]
Abstract
Thin films provide a versatile platform to tune electron correlations and explore new physics in strongly correlated materials. Epitaxially grown thin films of the alkali-doped fulleride K_{3+x}C_{60}, for example, exhibit intriguing phenomena, including Mott transitions and superconductivity, depending on dimensionality and doping. Surprisingly, in the trilayer case, a strong electron-hole doping asymmetry has been observed in the superconducting phase, which is absent in the three-dimensional bulk limit. Using density-functional theory plus dynamical mean-field theory, we show that this doping asymmetry results from a substantial charge reshuffling from the top layer to the middle layer. While the nominal filling per fullerene is close to n=3, the top layer rapidly switches to an n=2 insulating state upon hole doping, which implies a doping asymmetry of the superconducting gap. The interlayer charge transfer and layer-selective metal-insulator transition result from the interplay between crystal field splittings, strong Coulomb interactions, and an effectively negative Hund coupling. This peculiar charge reshuffling is absent in the monolayer system, which is an n=3 Mott insulator, as expected from the nominal filling.
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Affiliation(s)
- Changming Yue
- Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
| | - Yusuke Nomura
- Department of Applied Physics and Physico-Informatics, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Philipp Werner
- Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
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5
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Liu C, Kreisel A, Zhong S, Li Y, Andersen BM, Hirschfeld P, Wang J. Orbital-Selective High-Temperature Cooper Pairing Developed in the Two-Dimensional Limit. Nano Lett 2022; 22:3245-3251. [PMID: 35416679 DOI: 10.1021/acs.nanolett.1c04863] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
For multiband superconductors, the orbital multiplicity yields orbital differentiation in normal-state properties and can lead to orbital-selective spin-fluctuation Cooper pairing. The orbital-selective phenomenon has become increasingly pivotal in clarifying the pairing "enigma", particularly for multiband high-temperature superconductors. Meanwhile, in one-unit-cell (1-UC) FeSe/SrTiO3, since the standard electron-hole Fermi pocket nesting scenario is inapplicable, the actual pairing mechanism is subject to intense debate. Here, by measuring high-resolution Bogoliubov quasiparticle interference, we report observations of highly anisotropic magnetic Cooper pairing in 1-UC FeSe. Theoretically, it is important to incorporate orbitally selective effects of electronic correlations within a spin-fluctuation pairing calculation, where the dxy orbital becomes coherence-suppressed. The resulting pairing gap is compatible with the experimental findings, which suggests that high-Tc Cooper pairing with orbital selectivity applies to 2D-limit 1-UC FeSe. Our findings imply the general existence of orbital selectivity in iron-based superconductors and the universal significance of electron correlations in high-Tc superconductors.
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Affiliation(s)
- Chaofei Liu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, People's Republic of China
| | - Andreas Kreisel
- Institut für Theoretische Physik, Universität Leipzig, D-04103 Leipzig, Germany
| | - Shan Zhong
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, People's Republic of China
| | - Yu Li
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, People's Republic of China
| | - Brian M Andersen
- Niels Bohr Institute, University of Copenhagen, Jagtvej 128, DK-2200 Copenhagen, Denmark
| | - Peter Hirschfeld
- Department of Physics, University of Florida, Gainesville, Florida 32611, United States
| | - Jian Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, People's Republic of China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, People's Republic of China
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6
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Song Y, Chen Z, Zhang Q, Xu H, Lou X, Chen X, Xu X, Zhu X, Tao R, Yu T, Ru H, Wang Y, Zhang T, Guo J, Gu L, Xie Y, Peng R, Feng D. High temperature superconductivity at FeSe/LaFeO 3 interface. Nat Commun 2021; 12:5926. [PMID: 34635672 PMCID: PMC8505662 DOI: 10.1038/s41467-021-26201-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 09/15/2021] [Indexed: 11/09/2022] Open
Abstract
Enormous enhancement of superconducting pairing temperature (Tg) to 65 K in FeSe/SrTiO3 has made it a spotlight. Despite the effort of interfacial engineering, FeSe interfaced with TiOx remains the unique case in hosting high Tg, hindering a decisive understanding on the general mechanism and ways to further improving Tg. Here we constructed a new high-Tg interface, single-layer FeSe interfaced with FeOx-terminated LaFeO3. Large superconducting gap and diamagnetic response evidence that the superconducting pairing can emerge near 80 K, highest amongst all-known interfacial superconductors. Combining various techniques, we reveal interfacial charge transfer and strong interfacial electron-phonon coupling (EPC) in FeSe/LaFeO3, showing that the cooperative pairing mechanism works beyond FeSe-TiOx. Intriguingly, the stronger interfacial EPC than that in FeSe/SrTiO3 is likely induced by the stronger interfacial bonding in FeSe/LaFeO3, and can explain the higher Tg according to recent theoretical calculations, pointing out a workable route in designing new interfaces to achieve higher Tg.
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Affiliation(s)
- Yuanhe Song
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China
| | - Zheng Chen
- Department of Physics, Zhejiang University, 310027, Hangzhou, China
| | - Qinghua Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Haichao Xu
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China
- Shanghai Research Center for Quantum Sciences, 201315, Shanghai, China
| | - Xia Lou
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China
| | - Xiaoyang Chen
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China
| | - Xiaofeng Xu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Xuetao Zhu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Ran Tao
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China
| | - Tianlun Yu
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China
| | - Hao Ru
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China
| | - Yihua Wang
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China
- Shanghai Research Center for Quantum Sciences, 201315, Shanghai, China
| | - Tong Zhang
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China
- Shanghai Research Center for Quantum Sciences, 201315, Shanghai, China
| | - Jiandong Guo
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China.
| | - Lin Gu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China.
| | - Yanwu Xie
- Department of Physics, Zhejiang University, 310027, Hangzhou, China.
| | - Rui Peng
- Laboratory of Advanced Materials, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, 200438, Shanghai, China.
- Shanghai Research Center for Quantum Sciences, 201315, Shanghai, China.
| | - Donglai Feng
- Shanghai Research Center for Quantum Sciences, 201315, Shanghai, China.
- Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, 230026, Hefei, Anhui, China.
- Collaborative Innovation Center of Advanced Microstructures, 210093, Nanjing, China.
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7
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Liu C, Day RP, Li F, Roemer RL, Zhdanovich S, Gorovikov S, Pedersen TM, Jiang J, Lee S, Schneider M, Wong D, Dosanjh P, Walker FJ, Ahn CH, Levy G, Damascelli A, Sawatzky GA, Zou K. High-order replica bands in monolayer FeSe/SrTiO 3 revealed by polarization-dependent photoemission spectroscopy. Nat Commun 2021; 12:4573. [PMID: 34321473 DOI: 10.1038/s41467-021-24783-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Accepted: 07/09/2021] [Indexed: 11/13/2022] Open
Abstract
The mechanism of the enhanced superconductivity in monolayer FeSe/SrTiO3 has been enthusiastically studied and debated over the past decade. One specific observation has been taken to be of central importance: the replica bands in the photoemission spectrum. Although suggestive of electron-phonon interaction in the material, the essence of these spectroscopic features remains highly controversial. In this work, we conduct angle-resolved photoemission spectroscopy measurements on monolayer FeSe/SrTiO3 using linearly polarized photons. This configuration enables unambiguous characterization of the valence electronic structure with a suppression of the spectral background. We consistently observe high-order replica bands derived from various Fe 3d bands, similar to those observed on bare SrTiO3. The intensity of the replica bands is unexpectedly high and different between dxy and dyz bands. Our results provide new insights on the electronic structure of this high-temperature superconductor and the physical origin of the photoemission replica bands. The origin of the photoemission replica bands in monolayer FeSe/SrTiO3 remains controversial. Here, the authors perform angle-resolved photoemission spectroscopy with polarized photon on FeSe/SrTiO3 and observe high-order replica bands with high intensity from various Fe 3d bands, suggesting a mixed mechanism.
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8
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Zhang H, Zou Q, Li L. Tomonaga-Luttinger Liquid in the Topological Edge Channel of Multilayer FeSe. Nano Lett 2021; 21:6253-6260. [PMID: 34255523 DOI: 10.1021/acs.nanolett.1c02069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
A two-dimensional topological insulator exhibits helical edge states topologically protected against single-particle backscattering. Such protection breaks down, however, when electron-electron interactions are significant or when edge reconstruction occurs, leading to a suppressed density of states (DOS) at the Fermi level that follows universal scaling with temperature and energy, characteristic of Tomonaga-Luttinger liquid (TLL). Here, we grow multilayer FeSe on SrTiO3 by molecular beam epitaxy and observe robust edge states at both the {100}Se and the {110}Se steps using scanning tunneling microscopy/spectroscopy. We determine the DOS follows a power law, resulting in the Luttinger parameter K of 0.26 ± 0.02 and 0.43 ± 0.07 for the {100}Se and {110}Se edges, respectively. The smaller K for the {100}Se edge also indicates strong correlations, attributed to ferromagnetic ordering likely present due to checkerboard antiferromagnetic fluctuations in FeSe. These results demonstrate TLL in FeSe helical edge channels, providing an exciting model system for novel topological excitations arising from superconductivity and interacting helical edge states.
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Affiliation(s)
- Huimin Zhang
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Qiang Zou
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Lian Li
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
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9
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Faeth BD, Xie S, Yang S, Kawasaki JK, Nelson JN, Zhang S, Parzyck C, Mishra P, Li C, Jozwiak C, Bostwick A, Rotenberg E, Schlom DG, Shen KM. Interfacial Electron-Phonon Coupling Constants Extracted from Intrinsic Replica Bands in Monolayer FeSe/SrTiO_{3}. Phys Rev Lett 2021; 127:016803. [PMID: 34270322 DOI: 10.1103/physrevlett.127.016803] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Revised: 04/26/2021] [Accepted: 05/19/2021] [Indexed: 06/13/2023]
Abstract
The observation of replica bands by angle-resolved photoemission spectroscopy has ignited interest in the study of electron-phonon coupling at low carrier densities, particularly in monolayer FeSe/SrTiO_{3}, where the appearance of replica bands has motivated theoretical work suggesting that the interfacial coupling of electrons in the FeSe layer to optical phonons in the SrTiO_{3} substrate might contribute to the enhanced superconducting pairing temperature. Alternatively, it has also been recently proposed that such replica bands might instead originate from extrinsic final state losses associated with the photoemission process. Here, we perform a quantitative examination of replica bands in monolayer FeSe/SrTiO_{3}, where we are able to conclusively demonstrate that the replica bands are indeed signatures of intrinsic electron-boson coupling, and not associated with final state effects. A detailed analysis of the energy splittings and relative peak intensities between the higher-order replicas, as well as other self-energy effects, allows us to determine that the interfacial electron-phonon coupling in the system corresponds to a value of λ=0.19±0.02, providing valuable insights into the enhancement of superconductivity in monolayer FeSe/SrTiO_{3}. The methodology employed here can also serve as a new and general approach for making more rigorous and quantitative comparisons to theoretical calculations of electron-phonon interactions and coupling constants.
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Affiliation(s)
- Brendan D Faeth
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
| | - Saien Xie
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
| | - Shuolong Yang
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
- Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
| | - Jason K Kawasaki
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
| | - Jocienne N Nelson
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
| | - Shuyuan Zhang
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
| | - Christopher Parzyck
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
| | - Pramita Mishra
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
| | - Chen Li
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
| | - Christopher Jozwiak
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Aaron Bostwick
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Eli Rotenberg
- Advanced Light Source, E.O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Darrell G Schlom
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
- Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
| | - Kyle M Shen
- Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
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10
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Pelliciari J, Karakuzu S, Song Q, Arpaia R, Nag A, Rossi M, Li J, Yu T, Chen X, Peng R, García-Fernández M, Walters AC, Wang Q, Zhao J, Ghiringhelli G, Feng D, Maier TA, Zhou KJ, Johnston S, Comin R. Evolution of spin excitations from bulk to monolayer FeSe. Nat Commun 2021; 12:3122. [PMID: 34035254 DOI: 10.1038/s41467-021-23317-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 04/16/2021] [Indexed: 11/24/2022] Open
Abstract
In ultrathin films of FeSe grown on SrTiO3 (FeSe/STO), the superconducting transition temperature Tc is increased by almost an order of magnitude, raising questions on the pairing mechanism. As in other superconductors, antiferromagnetic spin fluctuations have been proposed to mediate SC making it essential to study the evolution of the spin dynamics of FeSe from the bulk to the ultrathin limit. Here, we investigate the spin excitations in bulk and monolayer FeSe/STO using resonant inelastic x-ray scattering (RIXS) and quantum Monte Carlo (QMC) calculations. Despite the absence of long-range magnetic order, bulk FeSe displays dispersive magnetic excitations reminiscent of other Fe-pnictides. Conversely, the spin excitations in FeSe/STO are gapped, dispersionless, and significantly hardened relative to its bulk counterpart. By comparing our RIXS results with simulations of a bilayer Hubbard model, we connect the evolution of the spin excitations to the Fermiology of the two systems revealing a remarkable reconfiguration of spin excitations in FeSe/STO, essential to understand the role of spin fluctuations in the pairing mechanism. Here, Pelliciari et al. present resonant inelastic X-ray scattering on monolayer samples of unconventional superconductor FeSe, finding evidence for gapped and dispersionless spin excitations. These experiments are very difficult due to the extremely small scattering volume of the FeSe monolayer.
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11
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Xu Y, Rong H, Wang Q, Wu D, Hu Y, Cai Y, Gao Q, Yan H, Li C, Yin C, Chen H, Huang J, Zhu Z, Huang Y, Liu G, Xu Z, Zhao L, Zhou XJ. Spectroscopic evidence of superconductivity pairing at 83 K in single-layer FeSe/SrTiO 3 films. Nat Commun 2021; 12:2840. [PMID: 33990574 PMCID: PMC8121788 DOI: 10.1038/s41467-021-23106-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 04/13/2021] [Indexed: 12/02/2022] Open
Abstract
Single-layer FeSe films grown on the SrTiO3 substrate (FeSe/STO) have attracted much attention because of their possible record-high superconducting critical temperature (Tc) and distinct electronic structures. However, it has been under debate on how high its Tc can really reach due to the inconsistency of the results from different measurements. Here we report spectroscopic evidence of superconductivity pairing at 83 K in single-layer FeSe/STO films. By preparing high-quality single-layer FeSe/STO films, we observe strong superconductivity-induced Bogoliubov back-bending bands that extend to rather high binding energy ~ 100 meV by high-resolution angle-resolved photoemission measurements. They provide a new definitive benchmark of superconductivity pairing that is directly observed up to 83 K. Moreover, we find that the pairing state can be further divided into two temperature regions. These results indicate that either Tc as high as 83 K is achievable, or there is a pseudogap formation from superconductivity fluctuation in single-layer FeSe/STO films. How high the superconducting transition temperature can reach in single layer FeSe/SrTiO3 films has been under debate. Here, the authors use Bogoliubov back-bending bands as a benchmark and demonstrate that superconductivity pairing can be realized up to 83 K in this system.
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Affiliation(s)
- Yu Xu
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Hongtao Rong
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Qingyan Wang
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China. .,University of Chinese Academy of Sciences, Beijing, China.
| | - Dingsong Wu
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Yong Hu
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Yongqing Cai
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Qiang Gao
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Hongtao Yan
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Cong Li
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Chaohui Yin
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Hao Chen
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Jianwei Huang
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
| | - Zhihai Zhu
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Yuan Huang
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Guodong Liu
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China.,Songshan Lake Materials Laboratory, Dongguan, China
| | - Zuyan Xu
- Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, China
| | - Lin Zhao
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China. .,University of Chinese Academy of Sciences, Beijing, China. .,Songshan Lake Materials Laboratory, Dongguan, China.
| | - X J Zhou
- National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China. .,University of Chinese Academy of Sciences, Beijing, China. .,Songshan Lake Materials Laboratory, Dongguan, China. .,Beijing Academy of Quantum Information Sciences, Beijing, China.
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12
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Qiu D, Gong C, Wang S, Zhang M, Yang C, Wang X, Xiong J. Recent Advances in 2D Superconductors. Adv Mater 2021; 33:e2006124. [PMID: 33768653 DOI: 10.1002/adma.202006124] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Revised: 10/22/2020] [Indexed: 06/12/2023]
Abstract
The emergence of superconductivity in 2D materials has attracted much attention and there has been rapid development in recent years because of their fruitful physical properties, such as high transition temperature (Tc ), continuous phase transition, and enhanced parallel critical magnetic field (Bc ). Tremendous efforts have been devoted to exploring different physical parameters to figure out the mechanisms behind the unexpected superconductivity phenomena, including adjusting the thickness of samples, fabricating various heterostructures, tuning the carrier density by electric field and chemical doping, and so on. Here, different types of 2D superconductivity with their unique characteristics are introduced, including the conventional Bardeen-Cooper-Schrieffer superconductivity in ultrathin films, high-Tc superconductivity in Fe-based and Cu-based 2D superconductors, unconventional superconductivity in newly discovered twist-angle bilayer graphene, superconductivity with enhanced Bc , and topological superconductivity. A perspective toward this field is then proposed based on academic knowledge from the recently reported literature. The aim is to provide researchers with a clear and comprehensive understanding about the newly developed 2D superconductivity and promote the development of this field much further.
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Affiliation(s)
- Dong Qiu
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Chuanhui Gong
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - SiShuang Wang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Miao Zhang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Chao Yang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Xianfu Wang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Jie Xiong
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
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13
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Zhang T, Bao W, Chen C, Li D, Lu Z, Hu Y, Yang W, Zhao D, Yan Y, Dong X, Wang QH, Zhang T, Feng D. Observation of Distinct Spatial Distributions of the Zero and Nonzero Energy Vortex Modes in (Li_{0.84}Fe_{0.16})OHFeSe. Phys Rev Lett 2021; 126:127001. [PMID: 33834795 DOI: 10.1103/physrevlett.126.127001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 01/18/2021] [Accepted: 03/02/2021] [Indexed: 06/12/2023]
Abstract
The energy and spatial distributions of vortex bound state in superconductors carry important information about superconducting pairing and the electronic structure. Although discrete vortex states, and sometimes a zero energy mode, had been observed in several iron-based superconductors, their spatial properties are rarely explored. In this study, we used low-temperature scanning tunneling microscopy to measure the vortex state of (Li,Fe)OHFeSe with high spatial resolution. We found that the nonzero energy states display clear spatial oscillations with a period corresponding to bulk Fermi wavelength; while in contrast, the zero energy mode does not show such oscillation, which suggests its distinct electronic origin. Furthermore, the oscillations of positive and negative energy states near E_{F} are found to be clearly out of phase. Based on a two-band model calculation, we show that our observation is more consistent with an s_{++} wave pairing in the bulk of (Li, Fe)OHFeSe, and superconducting topological states on the surface.
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Affiliation(s)
- Tianzhen Zhang
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
| | - Weicheng Bao
- National Laboratory of Solid State Microstructures & School of Physics, Nanjing University, Nanjing 210093, China
- Zhejiang University of Water Resources and Electric Power, Hangzhou 310018, China
| | - Chen Chen
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
| | - Dong Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zouyuwei Lu
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yining Hu
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
| | - Wentao Yang
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
| | - Dongming Zhao
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
| | - Yajun Yan
- Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Xiaoli Dong
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Qiang-Hua Wang
- National Laboratory of Solid State Microstructures & School of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Tong Zhang
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
- Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
| | - Donglai Feng
- Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
- Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
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14
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Abstract
FeSe is classed as a Hund’s metal, with a multiplicity of d bands near the Fermi level. Correlations in Hund’s metals mostly originate from the exchange parameter J, which can drive a strong orbital selectivity in the correlations. The Fe-chalcogens are the most strongly correlated of the Fe-based superconductors, with dxy the most correlated orbital. Yet little is understood whether and how such correlations directly affect the superconducting instability in Hund’s systems. By applying a recently developed ab initio theory, we show explicitly the connections between correlations in dxy and the superconducting critical temperature Tc. Starting from the ab initio results as a reference, we consider various kinds of excursions in parameter space around the reference to determine what controls Tc. We show small excursions in J can cause colossal changes in Tc. Additionally we consider changes in hopping by varying the Fe-Se bond length in bulk, in the free standing monolayer M-FeSe, and M-FeSe on a SrTiO3 substrate (M-FeSe/STO). The twin conditions of proximity of the dxy state to the Fermi energy, and the strength of J emerge as the primary criteria for incoherent spectral response and enhanced single- and two-particle scattering that in turn controls Tc. Using c-RPA, we show further that FeSe in monolayer form (M-FeSe) provides a natural mechanism to enhance J. We explain why M-FeSe/STO has a high Tc, whereas M-FeSe in isolation should not. Our study opens a paradigm for a unified understanding what controls Tc in bulk, layers, and interfaces of Hund’s metals by hole pocket and electron screening cloud engineering.
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15
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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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16
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Huang Y, Pan YH, Yang R, Bao LH, Meng L, Luo HL, Cai YQ, Liu GD, Zhao WJ, Zhou Z, Wu LM, Zhu ZL, Huang M, Liu LW, Liu L, Cheng P, Wu KH, Tian SB, Gu CZ, Shi YG, Guo YF, Cheng ZG, Hu JP, Zhao L, Yang GH, Sutter E, Sutter P, Wang YL, Ji W, Zhou XJ, Gao HJ. Universal mechanical exfoliation of large-area 2D crystals. Nat Commun 2020; 11:2453. [PMID: 32415180 PMCID: PMC7228924 DOI: 10.1038/s41467-020-16266-w] [Citation(s) in RCA: 166] [Impact Index Per Article: 41.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Accepted: 04/21/2020] [Indexed: 12/23/2022] Open
Abstract
Two-dimensional materials provide extraordinary opportunities for exploring phenomena arising in atomically thin crystals. Beginning with the first isolation of graphene, mechanical exfoliation has been a key to provide high-quality two-dimensional materials, but despite improvements it is still limited in yield, lateral size and contamination. Here we introduce a contamination-free, one-step and universal Au-assisted mechanical exfoliation method and demonstrate its effectiveness by isolating 40 types of single-crystalline monolayers, including elemental two-dimensional crystals, metal-dichalcogenides, magnets and superconductors. Most of them are of millimeter-size and high-quality, as shown by transfer-free measurements of electron microscopy, photo spectroscopies and electrical transport. Large suspended two-dimensional crystals and heterojunctions were also prepared with high-yield. Enhanced adhesion between the crystals and the substrates enables such efficient exfoliation, for which we identify a gold-assisted exfoliation method that underpins a universal route for producing large-area monolayers and thus supports studies of fundamental properties and potential application of two-dimensional materials.
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Affiliation(s)
- Yuan Huang
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- Songshan Lake Materials Laboratory, 523808, Dongguan, China
| | - Yu-Hao Pan
- Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Renmin University of China, 100872, Beijing, China
| | - Rong Yang
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- Songshan Lake Materials Laboratory, 523808, Dongguan, China
| | - Li-Hong Bao
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Lei Meng
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Hai-Lan Luo
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Yong-Qing Cai
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Guo-Dong Liu
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Wen-Juan Zhao
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Zhang Zhou
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Liang-Mei Wu
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Zhi-Li Zhu
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Ming Huang
- School of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Li-Wei Liu
- School of Information and Electronics, MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, Beijing Institute of Technology, 100081, Beijing, China
| | - Lei Liu
- College of Engineering, Peking University, 100871, Beijing, China
| | - Peng Cheng
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Ke-Hui Wu
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Shi-Bing Tian
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Chang-Zhi Gu
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - You-Guo Shi
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
| | - Yan-Feng Guo
- School of Physical Science and Technology, Shanghai Tech University, 201210, Shanghai, China
| | - Zhi Gang Cheng
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- Songshan Lake Materials Laboratory, 523808, Dongguan, China
- University of Chinese Academy of Sciences, 100049, Beijing, China
| | - Jiang-Ping Hu
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- Songshan Lake Materials Laboratory, 523808, Dongguan, China
- University of Chinese Academy of Sciences, 100049, Beijing, China
| | - Lin Zhao
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- Songshan Lake Materials Laboratory, 523808, Dongguan, China
- University of Chinese Academy of Sciences, 100049, Beijing, China
| | - Guan-Hua Yang
- Institute of Microelectronics of Chinese Academy of Sciences, 100029, Beijing, China
| | - Eli Sutter
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, United States
| | - Peter Sutter
- Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, United States.
| | - Ye-Liang Wang
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China
- School of Information and Electronics, MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, Beijing Institute of Technology, 100081, Beijing, China
| | - Wei Ji
- Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Renmin University of China, 100872, Beijing, China.
| | - Xing-Jiang Zhou
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China.
- Songshan Lake Materials Laboratory, 523808, Dongguan, China.
- University of Chinese Academy of Sciences, 100049, Beijing, China.
| | - Hong-Jun Gao
- Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China.
- University of Chinese Academy of Sciences, 100049, Beijing, China.
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17
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Xu X, Zhang S, Zhu X, Guo J. Superconductivity enhancement in FeSe/SrTiO 3: a review from the perspective of electron-phonon coupling. J Phys Condens Matter 2020; 32:343003. [PMID: 32241002 DOI: 10.1088/1361-648x/ab85f0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Single-layer FeSe films grown on SrTiO3, with the highest superconducting transition temperature (T C) among all the iron-based superconductors, serves as an ideal platform for studying the microscopic mechanisms of high-T C superconductivity. The significant role of interfacial coupling has been widely recognized, while the precise nature of the T C enhancement remains open. In this review, we focus on the investigations of the interfacial coupling in FeSe/SrTiO3 from the perspective of electron-phonon coupling (EPC). The main content will include an overview of the experimental measurements associated with different theoretical models and arguments about the EPC. Especially, besides the discussions of EPC based on the measurements of electronic states, we will emphasize the analyses based on phonon measurements. A uniform picture about the nature of the EPC and its relation to the T C enhancement in FeSe/SrTiO3 has still not achieved, which should be the key for further studies aiming to the in-depth understanding of high-T C superconductivity and the discovery of new superconductors with even enhanced T C.
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Affiliation(s)
- Xiaofeng Xu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China. School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
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18
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Chen C, Liu Q, Bao WC, Yan Y, Wang QH, Zhang T, Feng D. Observation of Discrete Conventional Caroli-de Gennes-Matricon States in the Vortex Core of Single-Layer FeSe/SrTiO_{3}. Phys Rev Lett 2020; 124:097001. [PMID: 32202862 DOI: 10.1103/physrevlett.124.097001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Revised: 02/09/2020] [Accepted: 02/12/2020] [Indexed: 06/10/2023]
Abstract
Using low-temperature scanning tunneling microscopy (STM), we studied the vortex states of single-layer FeSe film on a SrTiO_{3} (100) substrate, and the local behaviors of superconductivity at sample boundaries. We clearly observed multiple discrete Caroli-de Gennes-Matricon states in the vortex core, and quantitative analysis shows their energies well follow the formula: E=μΔ^{2}/E_{F}, where μ is a half integer (±1/2,±3/2,±5/2…) and Δ is the mean superconducting gap over the Fermi surface. Meanwhile, a fully gapped spectrum without states near zero bias is observed at the [110]_{Fe} oriented boundary of 1 and 2 ML FeSe films, and atomic step edge of 1 ML FeSe. Accompanied with theoretical calculations, our results indicate an s-wave pairing without sign change in the high-T_{C} FeSe/SrTiO_{3} superconductor.
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Affiliation(s)
- Chen Chen
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Qin Liu
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
- Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang, Sichuan 621908, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Wei-Cheng Bao
- National Laboratory of Solid State Microstructures & School of Physics, Nanjing University, Nanjing, 210093, China
- Zhejiang University of Water Resources and Electric Power, Hangzhou 310018, China
| | - Yajun Yan
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Qiang-Hua Wang
- National Laboratory of Solid State Microstructures & School of Physics, Nanjing University, Nanjing, 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Tong Zhang
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Donglai Feng
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200438, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
- Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
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19
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Liu C, Chen C, Liu X, Wang Z, Liu Y, Ye S, Wang Z, Hu J, Wang J. Zero-energy bound states in the high-temperature superconductors at the two-dimensional limit. Sci Adv 2020; 6:eaax7547. [PMID: 32232145 PMCID: PMC7096174 DOI: 10.1126/sciadv.aax7547] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Accepted: 01/06/2020] [Indexed: 05/25/2023]
Abstract
Majorana zero modes (MZMs) that obey the non-Abelian statistics have been intensively investigated for potential applications in topological quantum computing. The prevailing signals in tunneling experiments "fingerprinting" the existence of MZMs are the zero-energy bound states (ZEBSs). However, nearly all of the previously reported ZEBSs showing signatures of the MZMs are observed in difficult-to-fabricate heterostructures at very low temperatures and additionally require applied magnetic field. Here, by using in situ scanning tunneling spectroscopy, we detect the ZEBSs upon the interstitial Fe adatoms deposited on two different high-temperature superconducting one-unit-cell iron chalcogenides on SrTiO3(001). The spectroscopic results resemble the phenomenological characteristics of the MZMs inside the vortex cores of topological superconductors. Our experimental findings may extend the MZM explorations in connate topological superconductors toward an applicable temperature regime and down to the two-dimensional (2D) limit.
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Affiliation(s)
- Chaofei Liu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Cheng Chen
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Xiaoqiang Liu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Ziqiao Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Yi Liu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Shusen Ye
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Ziqiang Wang
- Department of Physics, Boston College, Chestnut Hill, MA 02467, USA
| | - Jiangping Hu
- Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Kavli Institute of Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Jian Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
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20
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Zhang RX, Cole WS, Wu X, Das Sarma S. Higher-Order Topology and Nodal Topological Superconductivity in Fe(Se,Te) Heterostructures. Phys Rev Lett 2019; 123:167001. [PMID: 31702343 DOI: 10.1103/physrevlett.123.167001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Revised: 08/28/2019] [Indexed: 06/10/2023]
Abstract
We show, theoretically, that a heterostructure of monolayer FeTe_{1-x}Se_{x}-a superconducting quantum spin Hall material-with a monolayer of FeTe-a bicollinear antiferromagnet-realizes a higher order topological superconductor phase characterized by emergent Majorana zero modes pinned to the sample corners. We provide a minimal effective model for this system, analyze the origin of higher order topology, and fully characterize the topological phase diagram. Despite the conventional s-wave pairing, we find a rather surprising emergence of a novel topological nodal superconductor in the phase diagram. Featured by edge-dependent Majorana flat bands, the topological nodal phase is protected by an antiferromagnetic chiral symmetry. We also discuss the experimental feasibility, the estimation of realistic model parameters, and the robustness of the Majorana corner modes against magnetic and potential disorder. Our work provides a new experimentally feasible high-temperature platform for both higher order topology and non-Abelian Majorana physics.
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Affiliation(s)
- Rui-Xing Zhang
- Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
| | - William S Cole
- Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
| | - Xianxin Wu
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland Campus Süd, Würzburg 97074, Germany
| | - S Das Sarma
- Condensed Matter Theory Center and Joint Quantum Institute, Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
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21
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Liu C, Wang Z, Gao Y, Liu X, Liu Y, Wang QH, Wang J. Spectroscopic Imaging of Quasiparticle Bound States Induced by Strong Nonmagnetic Scatterings in One-Unit-Cell FeSe/SrTiO_{3}. Phys Rev Lett 2019; 123:036801. [PMID: 31386432 DOI: 10.1103/physrevlett.123.036801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Indexed: 06/10/2023]
Abstract
The absence of holelike Fermi pockets in the heavily electron-doped iron selenides (HEDISs) challenges the s_{±}-wave pairing originally proposed for iron pnictides, which consists of opposite signs of the gap function on electron and hole pockets. While the HEDIS compounds have been investigated extensively, a consistent description of the superconducting pairing therein is still lacking. Here, by in situ scanning tunneling spectroscopy and theoretical calculations, we study the effects of strong scatterings from nonmagnetic Pb adatoms on the epitaxially grown HEDIS, one-unit-cell FeSe/SrTiO_{3}(001). Systematic tunneling spectra measured on the Pb adatoms show comprehensive signals of quasiparticle bound states, which can be well explained theoretically within the sign-reversing pairing scenarios. The finding implies that, in addition to previously detected phonons, spin fluctuations play an important role in driving the Cooper pairing in FeSe/SrTiO_{3}(001). The sign reversal in the gap function we revealed here is a significant ingredient in a unified understanding of the high-temperature superconductivity in HEDISs.
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Affiliation(s)
- Chaofei Liu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Ziqiao Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Yi Gao
- Center for Quantum Transport and Thermal Energy Science, Jiangsu Key Lab on Opto-Electronic Technology, School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China
| | - Xiaoqiang Liu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Yi Liu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Qiang-Hua Wang
- National Laboratory of Solid State Microstructures and School of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Jian Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
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22
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Liu C, Wang Z, Ye S, Chen C, Liu Y, Wang Q, Wang QH, Wang J. Detection of Bosonic Mode as a Signature of Magnetic Excitation in One-Unit-Cell FeSe on SrTiO 3. Nano Lett 2019; 19:3464-3472. [PMID: 31117746 DOI: 10.1021/acs.nanolett.9b00144] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
A "fingerprint" of Cooper pairing mediated by collective bosonic excitation mode is the reconstruction of the quasiparticle-density-of-states (DOS) spectrum with an additional "dip-hump" structure located outside the superconducting coherence peak. Here, we report an in situ scanning tunneling spectroscopy study of one-unit-cell (1-UC) FeSe film on a SrTiO3(001) substrate. In the quasiparticle-DOS spectrum, the bosonic excitation mode characterized by the dip-hump structure is detected outside the larger superconducting gap. Statistically, the excitation mode shows an anticorrelation with pairing strength in magnitude and yields an energy scale upper-bounded by twice the superconducting gap. The observation coincides with the characteristics of magnetic resonance in cuprates and iron-based superconductors. Furthermore, the local response of superconducting spectra to magnetically distinct Se defects all exhibits the induced in-gap quasiparticle bound states, indicating an unconventional sign-reversing pairing over the Fermi surface in 1-UC FeSe. These results clarify the magnetic nature of the bosonic excitation mode and reveal a signature of electron-magnetic-excitation coupling in 1-UC FeSe/SrTiO3(001) besides the previously established pairing channel of electron-phonon interaction.
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Affiliation(s)
- Chaofei Liu
- International Center for Quantum Materials, School of Physics , Peking University , Beijing 100871 , China
| | - Ziqiao Wang
- International Center for Quantum Materials, School of Physics , Peking University , Beijing 100871 , China
| | - Shusen Ye
- International Center for Quantum Materials, School of Physics , Peking University , Beijing 100871 , China
| | - Cheng Chen
- International Center for Quantum Materials, School of Physics , Peking University , Beijing 100871 , China
| | - Yi Liu
- International Center for Quantum Materials, School of Physics , Peking University , Beijing 100871 , China
| | - Qingyan Wang
- International Center for Quantum Materials, School of Physics , Peking University , Beijing 100871 , China
| | | | - Jian Wang
- International Center for Quantum Materials, School of Physics , Peking University , Beijing 100871 , China
- Collaborative Innovation Center of Quantum Matter , Beijing 100871 , China
- CAS Center for Excellence in Topological Quantum Computation , University of Chinese Academy of Sciences , Beijing 100190 , China
- Beijing Academy of Quantum Information Sciences , Beijing 100193 , China
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23
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Ge Z, Yan C, Zhang H, Agterberg D, Weinert M, Li L. Evidence for d-Wave Superconductivity in Single Layer FeSe/SrTiO 3 Probed by Quasiparticle Scattering Off Step Edges. Nano Lett 2019; 19:2497-2502. [PMID: 30916981 DOI: 10.1021/acs.nanolett.9b00135] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The de Gennes extrapolation length is a direction dependent measure of the spatial evolution of the pairing gap near the boundary of a superconductor and thus provides a viable means to probe its symmetry. It is expected to be infinite and isotropic for plain s-wave pairing, and finite and anisotropic for d-wave. Here, we synthesize single-layer FeSe films on SrTiO3(001) (STO) substrates by molecular beam epitaxy and measure the de Gennes extrapolation length by scanning tunneling microscopy/spectroscopy. We find a 40% reduction of the superconducting gap near specular [110]Fe edges, yielding an extrapolation length of 8.0 nm. However, near specular [010]Fe edges, the extrapolation length is nearly infinite. These findings are consistent with a phase changing pairing with 2-fold symmetry, indicating d-wave superconductivity. This is further supported by the presence of in-gap states near the specular [110]Fe edges, but not the [010]Fe edges. This work provides direct experimental evidence for d-wave superconductivity in single-layer FeSe/STO and demonstrates quasiparticle scattering at boundaries to be a viable phase sensitive probe of pairing symmetry in Fe-based superconductors.
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Affiliation(s)
- Zhuozhi Ge
- Department of Physics and Astronomy , West Virginia University , Morgantown , West Virginia 26506 , United States
- Department of Physics , University of Wisconsin , Milwaukee , Wisconsin 53211 , United States
| | - Chenhui Yan
- Department of Physics and Astronomy , West Virginia University , Morgantown , West Virginia 26506 , United States
| | - Huimin Zhang
- Department of Physics and Astronomy , West Virginia University , Morgantown , West Virginia 26506 , United States
| | - Daniel Agterberg
- Department of Physics , University of Wisconsin , Milwaukee , Wisconsin 53211 , United States
| | - Michael Weinert
- Department of Physics , University of Wisconsin , Milwaukee , Wisconsin 53211 , United States
| | - Lian Li
- Department of Physics and Astronomy , West Virginia University , Morgantown , West Virginia 26506 , United States
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24
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Song Q, Yu TL, Lou X, Xie BP, Xu HC, Wen CHP, Yao Q, Zhang SY, Zhu XT, Guo JD, Peng R, Feng DL. Evidence of cooperative effect on the enhanced superconducting transition temperature at the FeSe/SrTiO 3 interface. Nat Commun 2019; 10:758. [PMID: 30770805 DOI: 10.1038/s41467-019-08560-z] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2018] [Accepted: 01/18/2019] [Indexed: 11/16/2022] Open
Abstract
At the interface between monolayer FeSe films and SrTiO3 substrates the superconducting transition temperature (Tc) is unexpectedly high, triggering a surge of excitement. The mechanism for the Tc enhancement has been the central question, as it may present a new strategy for seeking out higher Tc materials. To reveal this enigmatic mechanism, by combining advances in high quality interface growth, 16O \documentclass[12pt]{minimal}
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\begin{document}$$\leftrightarrow$$\end{document}↔18O isotope substitution, and extensive data from angle resolved photoemission spectroscopy, we provide striking evidence that the high Tc in FeSe/SrTiO3 is the cooperative effect of the intrinsic pairing mechanism in the FeSe and interactions between the FeSe electrons and SrTiO3 phonons. Furthermore, our results point to the promising prospect that similar cooperation between different Cooper pairing channels may be a general framework to understand and design high-temperature superconductors. The mechanism of enhanced superconducting transition temperature (Tc) at the FeSe/SrTiO3 interface remains enigmatic. Here, Song and Yu et al. reveal the evidence of cooperation between intrinsic pairing interaction in FeSe and interfacial electron–phonon coupling to enhance the Tc at the FeSe/SrTiO3 interface.
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25
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Yang M, Yan C, Ma Y, Li L, Cen C. Light induced non-volatile switching of superconductivity in single layer FeSe on SrTiO 3 substrate. Nat Commun 2019; 10:85. [PMID: 30622274 PMCID: PMC6325130 DOI: 10.1038/s41467-018-08024-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 12/10/2018] [Indexed: 11/09/2022] Open
Abstract
The capability of controlling superconductivity by light is highly desirable for active quantum device applications. Since superconductors rarely exhibit strong photoresponses, and optically sensitive materials are often not superconducting, efficient coupling between these two characters can be very challenging in a single material. Here we show that, in FeSe/SrTiO3 heterostructures, the superconducting transition temperature in FeSe monolayer can be effectively raised by the interband photoexcitations in the SrTiO3 substrate. Attributed to a light induced metastable polar distortion uniquely enabled by the FeSe/SrTiO3 interface, this effect only requires a less than 50 µW cm-2 continuous-wave light field. The fast optical generation of superconducting zero resistance state is non-volatile but can be rapidly reversed by applying voltage pulses to the back of SrTiO3 substrate. The capability of switching FeSe repeatedly and reliably between normal and superconducting states demonstrate the great potential of making energy-efficient quantum optoelectronics at designed correlated interfaces.
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Affiliation(s)
- Ming Yang
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia, 26506, USA.,National Key Laboratory of Science and Technology on Power Sources, Tianjin Institute of Power Sources, Tianjin, 300384, P. R. China
| | - Chenhui Yan
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Yanjun Ma
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia, 26506, USA
| | - Lian Li
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia, 26506, USA.
| | - Cheng Cen
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia, 26506, USA.
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26
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Gao Y, Wang Y, Zhou T, Huang H, Wang QH. Possible Pairing Symmetry in the FeSe-Based Superconductors Determined by Quasiparticle Interference. Phys Rev Lett 2018; 121:267005. [PMID: 30636135 DOI: 10.1103/physrevlett.121.267005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2018] [Indexed: 06/09/2023]
Abstract
We study the momentum-integrated quasiparticle interference (QPI) in the FeSe-based superconductors. This method was recently proposed theoretically and has been applied to determine the pairing symmetry in these materials experimentally. Our findings suggest that, if the incipient bands and the superconducting (SC) pairing on them are taken into consideration, then the experimentally measured bound states and momentum-integrated QPI can be well fitted, even if the SC order parameter does not change sign on the Fermi surfaces. Therefore, we offer an alternative explanation to the experimental data, calling for more careful identification of the pairing symmetry that is important for the pairing mechanism.
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Affiliation(s)
- Yi Gao
- Center for Quantum Transport and Thermal Energy Science, School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China
- Jiangsu Key Lab on Opto-Electronic Technology, School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China
| | - Yuting Wang
- Center for Quantum Transport and Thermal Energy Science, School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China
| | - Tao Zhou
- Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, and School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, China
| | - Huaixiang Huang
- Department of Physics, Shanghai University, Shanghai, 200444, China
| | - Qiang-Hua Wang
- National Laboratory of Solid State Microstructures & School of Physics, Nanjing University, Nanjing, 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
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27
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Chen L, Zhao WW, Han RS. Resonance states near a quantum magnetic impurity in single-layer FeSe superconductors with d-wave symmetry. J Phys Condens Matter 2018; 30:305603. [PMID: 29911989 DOI: 10.1088/1361-648x/aacd37] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
In this work, we investigate the local density of states (LDOS) near a magnetic impurity in single-layer FeSe superconductors. The two-orbital model with spin-orbit coupling proposed in Agterberg et al (2017 Phys. Rev. Lett. 119 267001) is used to describe the FeSe superconductor. In the strong coupling regime, two impurity resonance peaks appear with opposite resonance energies in the LDOS spectral function. For strong spin-orbit coupling, the superconducting gap in this model is d-wave symmetric with nodes, the spatial distributions of the LDOS at the two resonance energies are fourfold symmetric, which reveals typical characteristic of d-wave pairing. When the spin-orbit coupling is not strong enough to close the superconducting gap, we find that the spatial distribution of the LDOS at one of the resonance energies manifests s-wave symmetry, while the pairing potential preserves d-wave symmetry. This result is consistent with previous experimental investigations.
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Affiliation(s)
- Liang Chen
- Mathematics and Physics Department, North China Electric Power University, Beijing, 102206, People's Republic of China
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28
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Agterberg DF, Shishidou T, O'Halloran J, Brydon PMR, Weinert M. Resilient Nodeless d-Wave Superconductivity in Monolayer FeSe. Phys Rev Lett 2017; 119:267001. [PMID: 29328694 DOI: 10.1103/physrevlett.119.267001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Indexed: 06/07/2023]
Abstract
Monolayer FeSe exhibits the highest transition temperature among the iron based superconductors and appears to be fully gapped, seemingly consistent with s-wave superconductivity. Here, we develop a theory for the superconductivity based on coupling to fluctuations of checkerboard magnetic order (which has the same translation symmetry as the lattice). The electronic states are described by a symmetry based k·p-like theory and naturally account for the states observed by angle resolved photoemission spectroscopy. We show that a prediction of this theory is that the resultant superconducting state is a fully gapped, nodeless, d-wave state. This state, which would usually have nodes, stays nodeless because, as seen experimentally, the relevant spin-orbit coupling has an energy scale smaller than the superconducting gap.
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Affiliation(s)
- D F Agterberg
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53201, USA
| | - T Shishidou
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53201, USA
| | - J O'Halloran
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53201, USA
| | - P M R Brydon
- Department of Physics, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
| | - M Weinert
- Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53201, USA
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29
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Abstract
Using the universal structure predictor algorithm, we proposed that two-dimensional MnB structures with p4mmm (α-MnB) and pmma (β-MnB) symmetries could be synthesized. This finding was verified by calculating the dynamical stability, molecular dynamics, and mechanical properties. The α-MnB had an in-plane stiffness Yx (=Yy) around 100 N/m while the β-Mn displayed an asymmetric mechanical stiffness of Yx = 186 N/m and Yy = 139 N/m. Both systems displayed a ferromagnetic ground state with metallic band structures. The calculated magnetic moments were 2.14 and 2.34 µB per Mn-B pair in the α-MnB and β-MnB. Furthermore, we investigated the potential superconductivity. In the α-MnB, we found the unique feature of Kohn anomaly at q~2kF in the diagonal direction of the Brillouin zone. The β-MnB phonon spectra showed a valley of degenerated localized softening vibration modes at the edge of the Brillouin zone. The ZA and LA phonon branches in this valley induced the largest contribution to electron-phonon coupling strength. The calculated total electron-phonon coupling parameters were 1.20 and 0.89 in α-MnB and β-MnB systems. Overall, we predict that the α-MnB and β-MnB systems can display 2D ferromagnetic superconducting states with the estimated critical temperatures of Tc ≈ 10−13 K.
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30
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Ren M, Yan Y, Niu X, Tao R, Hu D, Peng R, Xie B, Zhao J, Zhang T, Feng DL. Superconductivity across Lifshitz transition and anomalous insulating state in surface K-dosed (Li 0.8Fe 0.2OH)FeSe. Sci Adv 2017; 3:e1603238. [PMID: 28740865 PMCID: PMC5510993 DOI: 10.1126/sciadv.1603238] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 05/26/2017] [Indexed: 06/07/2023]
Abstract
In iron-based superconductors, understanding the relation between superconductivity and electronic structure upon doping is crucial for exploring the pairing mechanism. Recently, it was found that, in iron selenide (FeSe), enhanced superconductivity (Tc of more than 40 K) can be achieved via electron doping, with the Fermi surface only comprising M-centered electron pockets. By using surface K dosing, scanning tunneling microscopy/spectroscopy, and angle-resolved photoemission spectroscopy, we studied the electronic structure and superconductivity of (Li0.8Fe0.2OH)FeSe in the deep electron-doped regime. We find that a Γ-centered electron band, which originally lies above the Fermi level (EF), can be continuously tuned to cross EF and contribute a new electron pocket at Γ. When this Lifshitz transition occurs, the superconductivity in the M-centered electron pocket is slightly suppressed, and a possible superconducting gap with a small size (up to ~5 meV) and a dome-like doping dependence is observed on the new Γ electron pocket. Upon further K dosing, the system eventually evolves into an insulating state. Our findings provide new clues to understand superconductivity versus Fermi surface topology and the correlation effect in FeSe-based superconductors.
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Affiliation(s)
- Mingqiang Ren
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
| | - Yajun Yan
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
| | - Xiaohai Niu
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
| | - Ran Tao
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
| | - Die Hu
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
| | - Rui Peng
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
| | - Binping Xie
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Jun Zhao
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Tong Zhang
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Dong-Lai Feng
- State Key Laboratory of Surface Physics, Department of Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
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31
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Abstract
Since the dramatic enhancement of the superconducting transition temperature (T c) was reported in a one-unit-cell FeSe film grown on a SrTiO3 substrate (1-UC FeSe/STO) by molecular beam epitaxy (MBE), related research on this system has become a new frontier in condensed matter physics. In this paper, we present a brief review on this rapidly developing field, mainly focusing on the superconducting properties of 1-UC FeSe/STO. Experimental evidence for high-temperature superconductivity in 1-UC FeSe/STO, including direct evidence revealed by transport and diamagnetic measurements, as well as other evidence from scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), are overviewed. The potential mechanisms of the enhanced superconductivity are also discussed. There are accumulating arguments to suggest that the strengthened Cooper pairing in 1-UC FeSe/STO originates from the interface effects, specifically the charge transfer and coupling to phonon modes in the TiO2 plane. The study of superconductivity in 1-UC FeSe/STO not only sheds new light on the mechanism of high-temperature superconductors with layered structures, but also provides an insight into the exploration of new superconductors by interface engineering.
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Affiliation(s)
- Ziqiao Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, People's Republic of China
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32
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Shi X, Han ZQ, Peng XL, Richard P, Qian T, Wu XX, Qiu MW, Wang SC, Hu JP, Sun YJ, Ding H. Enhanced superconductivity accompanying a Lifshitz transition in electron-doped FeSe monolayer. Nat Commun 2017; 8:14988. [PMID: 28422183 PMCID: PMC5399296 DOI: 10.1038/ncomms14988] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 02/20/2017] [Indexed: 11/29/2022] Open
Abstract
The origin of enhanced superconductivity over 50 K in the recently discovered FeSe monolayer films grown on SrTiO3 (STO), as compared to 8 K in bulk FeSe, is intensely debated. As with the ferrochalcogenides AxFe2−ySe2 and potassium-doped FeSe, which also have a relatively high-superconducting critical temperature (Tc), the Fermi surface (FS) of the FeSe/STO monolayer films is free of hole-like FS, suggesting that a Lifshitz transition by which these hole FSs vanish may help increasing Tc. However, the fundamental reasons explaining this increase of Tc remain unclear. Here we report a 15 K jump of Tc accompanying a second Lifshitz transition characterized by the emergence of an electron pocket at the Brillouin zone centre, which is triggered by high-electron doping following in situ deposition of potassium on FeSe/STO monolayer films. Our results suggest that the pairing interactions are orbital dependent in generating enhanced superconductivity in FeSe. The origin of superconductivity enhancement in FeSe monolayer grown on SrTiO3 compared to bulk FeSe is still a debated issue. Here, Shi et al. report a further 15 K jump of Tc accompanying a second Lifshitz transition triggered by electron doping in FeSe/SrTiO3 monolayer films.
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Affiliation(s)
- X Shi
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Z-Q Han
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,Department of Physics, Beijing Key Laboratory of Opto-Electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, China
| | - X-L Peng
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - P Richard
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,Collaborative Innovation Center of Quantum Matter, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - T Qian
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,Collaborative Innovation Center of Quantum Matter, Beijing 100190, China
| | - X-X Wu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - M-W Qiu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - S C Wang
- Department of Physics, Beijing Key Laboratory of Opto-Electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, China
| | - J P Hu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,Collaborative Innovation Center of Quantum Matter, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Y-J Sun
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - H Ding
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.,Collaborative Innovation Center of Quantum Matter, Beijing 100190, China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
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33
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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 DOI: 10.1038/srep44024] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [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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34
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Kang J, Fernandes RM. Superconductivity in FeSe Thin Films Driven by the Interplay between Nematic Fluctuations and Spin-Orbit Coupling. Phys Rev Lett 2016; 117:217003. [PMID: 27911515 DOI: 10.1103/physrevlett.117.217003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Indexed: 06/06/2023]
Abstract
The origin of the high-temperature superconducting state observed in FeSe thin films, whose phase diagram displays no sign of magnetic order, remains a hotly debated topic. Here we investigate whether fluctuations arising due to the proximity to a nematic phase, which is observed in the phase diagram of this material, can promote superconductivity. We find that nematic fluctuations alone promote a highly degenerate pairing state, in which both s-wave and d-wave symmetries are equally favored, and T_{c} is consequently suppressed. However, the presence of a sizable spin-orbit coupling or inversion symmetry breaking at the film interface lifts this harmful degeneracy and selects the s-wave state, in agreement with recent experimental proposals. The resulting gap function displays a weak anisotropy, which agrees with experiments in monolayer FeSe and intercalated Li_{1-x}(OH)_{x}FeSe.
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Affiliation(s)
- Jian Kang
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Rafael M Fernandes
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
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35
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Abstract
Observations of robust superconductivity in some of the iron based superconductors in the vicinity of a Lifshitz point where a spin density wave instability is suppressed as the hole band drops below the Fermi energy raise questions for spin-fluctuation theories. Here we discuss spin-fluctuation pairing for a bilayer Hubbard model, which goes through such a Lifshitz transition. We find s± pairing with a transition temperature that peaks beyond the Lifshitz point and a gap function that has essentially the same magnitude but opposite sign on the incipient hole band as it does on the electron band that has a Fermi surface.
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Affiliation(s)
- Vivek Mishra
- Joint Institute of Computational Sciences, University of Tennessee, Knoxville, TN-37996, USA
| | - Douglas J Scalapino
- Department of Physics, University of California, Santa Barbara, CA-93106, USA
| | - Thomas A Maier
- Computer Science and Mathematics Division &Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN-37831, USA
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36
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Li ZX, Wang F, Yao H, Lee DH. What makes the Tc of monolayer FeSe on SrTiO 3 so high: a sign-problem-free quantum Monte Carlo study. Sci Bull (Beijing) 2016; 61:925-930. [PMID: 27398243 PMCID: PMC4914519 DOI: 10.1007/s11434-016-1087-x] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 04/18/2016] [Accepted: 04/18/2016] [Indexed: 11/29/2022]
Abstract
Monolayer FeSe films grown on SrTiO3 (STO) substrate show superconducting gap-opening temperatures (\documentclass[12pt]{minimal}
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\begin{document}$$T_{\mathrm{c}}$$\end{document}Tc) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based superconductors. Angle-resolved photoemission spectroscopy observed “replica bands” suggesting the importance of the interaction between FeSe electrons and STO phonons. These facts rejuvenated the quest for \documentclass[12pt]{minimal}
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\begin{document}$$T_{{\mathrm{c}}}$$\end{document}Tc enhancement mechanisms in iron-based, especially iron-chalcogenide, superconductors. Here, we perform the first numerically-exact sign-problem-free quantum Monte Carlo simulations to iron-based superconductors. We (1) study the electronic pairing mechanism intrinsic to heavily electron doped FeSe films, and (2) examine the effects of electron–phonon interaction between FeSe and STO as well as nematic fluctuations on \documentclass[12pt]{minimal}
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\begin{document}$$T_{{\mathrm{c}}}$$\end{document}Tc. Armed with these results, we return to the question “what makes the \documentclass[12pt]{minimal}
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\begin{document}$$T_{{\mathrm{c}}}$$\end{document}Tc of monolayer FeSe on SrTiO3 so high?” in the conclusion and discussions.
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Affiliation(s)
- Zi-Xiang Li
- />Institute for Advanced Study, Tsinghua University, Beijing, 100084 China
| | - Fa Wang
- />International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871 China
- />Collaborative Innovation Center of Quantum Matter, Beijing, 100871 China
| | - Hong Yao
- />Institute for Advanced Study, Tsinghua University, Beijing, 100084 China
- />Collaborative Innovation Center of Quantum Matter, Beijing, 100871 China
| | - Dung-Hai Lee
- />Department of Physics, University of California, Berkeley, CA 94720 USA
- />Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA
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