1
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Yu Y, Cheng M, Tao Z, Han W, Du G, Guo Y, Shi J, Chen Y. Phase-Modulated Elastic Properties of 2D Magnetic FeTe: Hexagonal and Tetragonal Polymorphs. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024; 20:e2308357. [PMID: 38050942 DOI: 10.1002/smll.202308357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 11/01/2023] [Indexed: 12/07/2023]
Abstract
2D layered magnets, such as iron chalcogenides, have emerged these years as a new family of unconventional superconductors and provided the key insights to understand the phonon-electron interaction and pairing mechanism. Their mechanical properties are of strategic importance for the potential applications in spintronics and optoelectronics. However, there is still a lack of efficient approach to tune the elastic modulus despite the extensive studies. Herein, the modulated elastic modulus of 2D magnetic FeTe and its thickness-dependence is reported via phase engineering. The grown 2D FeTe by chemical vapor deposition can present various polymorphs, that is tetragonal FeTe (t-FeTe, antiferromagnetic) and hexagonal FeTe (h-FeTe, ferromagnetic). The measured Young's modulus of t-FeTe by nanoindentation method shows an obvious thickness-dependence, from 290.9 ± 9.2 to 113.0 ± 8.7 GPa when the thicknesses increased from 13.2 to 42.5 nm, respectively. In comparison, the elastic modulus of h-FeTe remains unchanged. These results can shed light on the efficient modulation of mechanical properties of 2D magnetic materials and pave the avenues for their practical applications in nanodevices.
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Affiliation(s)
- Yunfei Yu
- School of Aerospace Engineering, Beijing Institute of Technology, Beijing, 100081, P. R. China
| | - Mo Cheng
- The Institute for Advanced Studies, Wuhan University, Wuhan, 430072, P. R. China
| | - Zicheng Tao
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 200031, P. R. China
- ShanghaiTech Laboratory for Topological Physics, Shanghai, 201210, P. R. China
| | - Wuxiao Han
- School of Aerospace Engineering, Beijing Institute of Technology, Beijing, 100081, P. R. China
| | - Guoshuai Du
- School of Aerospace Engineering, Beijing Institute of Technology, Beijing, 100081, P. R. China
| | - Yanfeng Guo
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 200031, P. R. China
- ShanghaiTech Laboratory for Topological Physics, Shanghai, 201210, P. R. China
| | - Jianping Shi
- The Institute for Advanced Studies, Wuhan University, Wuhan, 430072, P. R. China
| | - Yabin Chen
- School of Aerospace Engineering, Beijing Institute of Technology, Beijing, 100081, P. R. China
- Advanced Research Institute of Multidisciplinary Sciences, Beijing Institute of Technology, Beijing, 100081, P. R. China
- BIT Chongqing Institute of Microelectronics and Microsystems, Chongqing, 400030, P. R. China
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2
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Yi H, Zhao YF, Chan YT, Cai J, Mei R, Wu X, Yan ZJ, Zhou LJ, Zhang R, Wang Z, Paolini S, Xiao R, Wang K, Richardella AR, Singleton J, Winter LE, Prokscha T, Salman Z, Suter A, Balakrishnan PP, Grutter AJ, Chan MHW, Samarth N, Xu X, Wu W, Liu CX, Chang CZ. Interface-induced superconductivity in magnetic topological insulators. Science 2024; 383:634-639. [PMID: 38330133 DOI: 10.1126/science.adk1270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Accepted: 01/10/2024] [Indexed: 02/10/2024]
Abstract
The interface between two different materials can show unexpected quantum phenomena. In this study, we used molecular beam epitaxy to synthesize heterostructures formed by stacking together two magnetic materials, a ferromagnetic topological insulator (TI) and an antiferromagnetic iron chalcogenide (FeTe). We observed emergent interface-induced superconductivity in these heterostructures and demonstrated the co-occurrence of superconductivity, ferromagnetism, and topological band structure in the magnetic TI layer-the three essential ingredients of chiral topological superconductivity (TSC). The unusual coexistence of ferromagnetism and superconductivity is accompanied by a high upper critical magnetic field that exceeds the Pauli paramagnetic limit for conventional superconductors at low temperatures. These magnetic TI/FeTe heterostructures with robust superconductivity and atomically sharp interfaces provide an ideal wafer-scale platform for the exploration of chiral TSC and Majorana physics.
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Affiliation(s)
- Hemian Yi
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Yi-Fan Zhao
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Ying-Ting Chan
- Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA
| | - Jiaqi Cai
- Department of Physics, University of Washington, Seattle, WA 98195, USA
| | - Ruobing Mei
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Xianxin Wu
- CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Zi-Jie Yan
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Ling-Jie Zhou
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Ruoxi Zhang
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Zihao Wang
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Stephen Paolini
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Run Xiao
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Ke Wang
- Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
| | - Anthony R Richardella
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
- Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
| | - John Singleton
- National High Magnetic Field Laboratory, Los Alamos, NM 87544, USA
| | - Laurel E Winter
- National High Magnetic Field Laboratory, Los Alamos, NM 87544, USA
| | - Thomas Prokscha
- Laboratory for Muon Spectroscopy, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
| | - Zaher Salman
- Laboratory for Muon Spectroscopy, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
| | - Andreas Suter
- Laboratory for Muon Spectroscopy, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
| | - Purnima P Balakrishnan
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Alexander J Grutter
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
| | - Moses H W Chan
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Nitin Samarth
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
- Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA 98195, USA
- Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA
| | - Weida Wu
- Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854, USA
| | - Chao-Xing Liu
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
| | - Cui-Zu Chang
- Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA
- Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA
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3
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Liu Y, Wei T, He G, Zhang Y, Wang Z, Wang J. Pair density wave state in a monolayer high-T c iron-based superconductor. Nature 2023; 618:934-939. [PMID: 37380693 DOI: 10.1038/s41586-023-06072-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Accepted: 04/11/2023] [Indexed: 06/30/2023]
Abstract
The pair density wave (PDW) is an extraordinary superconducting state in which Cooper pairs carry non-zero momentum1,2. Evidence for the existence of intrinsic PDW order in high-temperature (high-Tc) cuprate superconductors3,4 and kagome superconductors5 has emerged recently. However, the PDW order in iron-based high-Tc superconductors has not been observed experimentally. Here, using scanning tunnelling microscopy and spectroscopy, we report the discovery of the PDW state in monolayer iron-based high-Tc Fe(Te,Se) films grown on SrTiO3(001) substrates. The PDW state with a period of λ ≈ 3.6aFe (aFe is the distance between neighbouring Fe atoms) is observed at the domain walls by the spatial electronic modulations of the local density of states, the superconducting gap and the π-phase shift boundaries of the PDW around the vortices of the intertwined charge density wave order. The discovery of the PDW state in the monolayer Fe(Te,Se) film provides a low-dimensional platform to study the interplay between the correlated electronic states and unconventional Cooper pairing in high-Tc superconductors.
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Affiliation(s)
- Yanzhao Liu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China
| | - Tianheng Wei
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China
| | - Guanyang He
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China
| | - Yi Zhang
- Department of Physics, Shanghai University, Shanghai, China
| | - Ziqiang Wang
- Department of Physics, Boston College, Chestnut Hill, MA, USA.
| | - Jian Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China.
- Collaborative Innovation Center of Quantum Matter, Beijing, China.
- Hefei National Laboratory, Hefei, China.
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, China.
- Beijing Academy of Quantum Information Sciences, Beijing, China.
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4
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Grigoriev PD, Kochev VD, Orlov AP, Frolov AV, Sinchenko AA. Inhomogeneous Superconductivity Onset in FeSe Studied by Transport Properties. MATERIALS (BASEL, SWITZERLAND) 2023; 16:1840. [PMID: 36902961 PMCID: PMC10003944 DOI: 10.3390/ma16051840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/15/2023] [Revised: 02/16/2023] [Accepted: 02/21/2023] [Indexed: 06/18/2023]
Abstract
Heterogeneous superconductivity onset is a common phenomenon in high-Tc superconductors of both the cuprate and iron-based families. It is manifested by a fairly wide transition from the metallic to zero-resistance states. Usually, in these strongly anisotropic materials, superconductivity (SC) first appears as isolated domains. This leads to anisotropic excess conductivity above Tc, and the transport measurements provide valuable information about the SC domain structure deep within the sample. In bulk samples, this anisotropic SC onset gives an approximate average shape of SC grains, while in thin samples, it also indicates the average size of SC grains. In this work, both interlayer and intralayer resistivity were measured as a function of temperature in FeSe samples of various thicknesses. To measure the interlayer resistivity, FeSe mesa structures oriented across the layers were fabricated using FIB. As the sample thickness decreases, a significant increase in superconducting transition temperature Tc is observed: Tc raises from 8 K in bulk material to 12 K in microbridges of thickness ∼40 nm. We applied analytical and numerical calculations to analyze these and earlier data and find the aspect ratio and size of the SC domains in FeSe consistent with our resistivity and diamagnetic response measurements. We propose a simple and fairly accurate method for estimating the aspect ratio of SC domains from Tc anisotropy in samples of various small thicknesses. The relationship between nematic and superconducting domains in FeSe is discussed. We also generalize the analytical formulas for conductivity in heterogeneous anisotropic superconductors to the case of elongated SC domains of two perpendicular orientations with equal volume fractions, corresponding to the nematic domain structure in various Fe-based superconductors.
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Affiliation(s)
- Pavel D. Grigoriev
- L.D. Landau Institute for Theoretical Physics, 142432 Chernogolovka, Russia
- Department of Theoretical Physics and Quantum Technologies, National University of Science and Technology ”MISiS”, 119049 Moscow, Russia
- P.N. Lebedev Physical Institute of RAS, 119991 Moscow, Russia
| | - Vladislav D. Kochev
- Department of Theoretical Physics and Quantum Technologies, National University of Science and Technology ”MISiS”, 119049 Moscow, Russia
| | - Andrey P. Orlov
- Kotel’nikov Institute of Radioengineering and Electronics of RAS, 125009 Moscow, Russia
- Institute of Nanotechnology of Microelectronics of RAS, 115487 Moscow, Russia
| | - Aleksei V. Frolov
- Kotel’nikov Institute of Radioengineering and Electronics of RAS, 125009 Moscow, Russia
| | - Alexander A. Sinchenko
- Kotel’nikov Institute of Radioengineering and Electronics of RAS, 125009 Moscow, Russia
- Laboratoire de Physique des Solides, Universite Paris-Saclay, 91405 Orsay, France
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5
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On the electron pairing mechanism of copper-oxide high temperature superconductivity. Proc Natl Acad Sci U S A 2022; 119:e2207449119. [PMID: 36067325 PMCID: PMC9477408 DOI: 10.1073/pnas.2207449119] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The elementary CuO2 plane sustaining cuprate high-temperature superconductivity occurs typically at the base of a periodic array of edge-sharing CuO5 pyramids. Virtual transitions of electrons between adjacent planar Cu and O atoms, occurring at a rate t/ℏ and across the charge-transfer energy gap [Formula: see text], generate "superexchange" spin-spin interactions of energy [Formula: see text] in an antiferromagnetic correlated-insulator state. However, hole doping this CuO2 plane converts this into a very-high-temperature superconducting state whose electron pairing is exceptional. A leading proposal for the mechanism of this intense electron pairing is that, while hole doping destroys magnetic order, it preserves pair-forming superexchange interactions governed by the charge-transfer energy scale [Formula: see text]. To explore this hypothesis directly at atomic scale, we combine single-electron and electron-pair (Josephson) scanning tunneling microscopy to visualize the interplay of [Formula: see text] and the electron-pair density nP in Bi2Sr2CaCu2O8+x. The responses of both [Formula: see text] and nP to alterations in the distance δ between planar Cu and apical O atoms are then determined. These data reveal the empirical crux of strongly correlated superconductivity in CuO2, the response of the electron-pair condensate to varying the charge-transfer energy. Concurrence of predictions from strong-correlation theory for hole-doped charge-transfer insulators with these observations indicates that charge-transfer superexchange is the electron-pairing mechanism of superconductive Bi2Sr2CaCu2O8+x.
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6
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Abstract
Electron-pair density wave (PDW) states are now an intense focus of research in the field of cuprate correlated superconductivity. PDWs exhibit periodically modulating superconductive electron pairing that can be visualized directly using scanned Josephson tunneling microscopy (SJTM). Although from theory, intertwining the d-wave superconducting (DSC) and PDW order parameters allows a plethora of global electron-pair orders to appear, which one actually occurs in the various cuprates is unknown. Here, we use SJTM to visualize the interplay of PDW and DSC states in Bi2Sr2CaCu2O8+x at a carrier density where the charge density wave modulations are virtually nonexistent. Simultaneous visualization of their amplitudes reveals that the intertwined PDW and DSC are mutually attractive states. Then, by separately imaging the electron-pair density modulations of the two orthogonal PDWs, we discover a robust nematic PDW state. Its spatial arrangement entails Ising domains of opposite nematicity, each consisting primarily of unidirectional and lattice commensurate electron-pair density modulations. Further, we demonstrate by direct imaging that the scattering resonances identifying Zn impurity atom sites occur predominantly within boundaries between these domains. This implies that the nematic PDW state is pinned by Zn atoms, as was recently proposed [Lozano et al., Phys. Rev. B 103, L020502 (2021)]. Taken in combination, these data indicate that the PDW in Bi2Sr2CaCu2O8+x is a vestigial nematic pair density wave state [Agterberg et al. Phys. Rev. B 91, 054502 (2015); Wardh and Granath arXiv:2203.08250].
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7
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Cheng M, Zhao X, Zeng Y, Wang P, Wang Y, Wang T, Pennycook SJ, He J, Shi J. Phase-Tunable Synthesis and Etching-Free Transfer of Two-Dimensional Magnetic FeTe. ACS NANO 2021; 15:19089-19097. [PMID: 34697943 DOI: 10.1021/acsnano.1c05738] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Two-dimensional (2D) Fe-chalcogenides (e.g., FeS, FeSe, and FeTe, etc.) have sparked extensive interest due to their rich phase diagrams including superconductivity, magnetism, and topological state, as well as versatile applications in electronic devices and energy related fields. However, the phase-tunable synthesis and green transfer of such fascinating materials still remain challenging. Herein, we develop a temperature-mediated chemical vapor deposition (CVD) approach to grow ultrathin nonlayered hexagonal and layered tetragonal FeTe nanosheets on mica substrates, with their thicknesses down to ∼2.3 and ∼4.0 nm, respectively. Interestingly, we have observed exciting ferromagnetism with the Curie temperature approaching ∼300 K and high conductivity (∼1.96 × 105 S m-1) in 2D hexagonal FeTe. More significantly, we have designed a swift, high-efficiency, and etching-free method for the transfer of 2D FeTe nanosheets onto arbitrary substrates, and such a transfer strategy enables the cyclic utilization of growth substrates. These results should propel the further development of phase-tunable synthesis and green transfer of 2D Fe-chalcogenides, as well as their potential applications in spintronic devices.
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Affiliation(s)
- Mo Cheng
- The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
| | - Xiaoxu Zhao
- School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
| | - Yan Zeng
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Peng Wang
- The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
| | - Yuzhu Wang
- The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
| | - Ti Wang
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Stephen John Pennycook
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jun He
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, and School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Jianping Shi
- The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
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8
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Chen H, Yang H, Hu B, Zhao Z, Yuan J, Xing Y, Qian G, Huang Z, Li G, Ye Y, Ma S, Ni S, Zhang H, Yin Q, Gong C, Tu Z, Lei H, Tan H, Zhou S, Shen C, Dong X, Yan B, Wang Z, Gao HJ. Roton pair density wave in a strong-coupling kagome superconductor. Nature 2021; 599:222-228. [PMID: 34587621 DOI: 10.1038/s41586-021-03983-5] [Citation(s) in RCA: 103] [Impact Index Per Article: 34.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Accepted: 09/01/2021] [Indexed: 02/08/2023]
Abstract
The transition metal kagome lattice materials host frustrated, correlated and topological quantum states of matter1-9. Recently, a new family of vanadium-based kagome metals, AV3Sb5 (A = K, Rb or Cs), with topological band structures has been discovered10,11. These layered compounds are nonmagnetic and undergo charge density wave transitions before developing superconductivity at low temperatures11-19. Here we report the observation of unconventional superconductivity and a pair density wave (PDW) in CsV3Sb5 using scanning tunnelling microscope/spectroscopy and Josephson scanning tunnelling spectroscopy. We find that CsV3Sb5 exhibits a V-shaped pairing gap Δ ~ 0.5 meV and is a strong-coupling superconductor (2Δ/kBTc ~ 5) that coexists with 4a0 unidirectional and 2a0 × 2a0 charge order. Remarkably, we discover a 3Q PDW accompanied by bidirectional 4a0/3 spatial modulations of the superconducting gap, coherence peak and gap depth in the tunnelling conductance. We term this novel quantum state a roton PDW associated with an underlying vortex-antivortex lattice that can account for the observed conductance modulations. Probing the electronic states in the vortex halo in an applied magnetic field, in strong field that suppresses superconductivity and in zero field above Tc, reveals that the PDW is a primary state responsible for an emergent pseudogap and intertwined electronic order. Our findings show striking analogies and distinctions to the phenomenology of high-Tc cuprate superconductors, and provide groundwork for understanding the microscopic origin of correlated electronic states and superconductivity in vanadium-based kagome metals.
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Affiliation(s)
- Hui Chen
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China.,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, People's Republic of China.,Songshan Lake Materials Laboratory, Dongguan, People's Republic of China
| | - Haitao Yang
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China.,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, People's Republic of China.,Songshan Lake Materials Laboratory, Dongguan, People's Republic of China
| | - Bin Hu
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Zhen Zhao
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Jie Yuan
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Yuqing Xing
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Guojian Qian
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Zihao Huang
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Geng Li
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China.,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Yuhan Ye
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Sheng Ma
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Shunli Ni
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Hua Zhang
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Qiangwei Yin
- Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Department of Physics, Renmin University of China, Beijing, People's Republic of China
| | - Chunsheng Gong
- Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Department of Physics, Renmin University of China, Beijing, People's Republic of China
| | - Zhijun Tu
- Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Department of Physics, Renmin University of China, Beijing, People's Republic of China
| | - Hechang Lei
- Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Department of Physics, Renmin University of China, Beijing, People's Republic of China
| | - Hengxin Tan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Sen Zhou
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China.,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, People's Republic of China.,CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Chengmin Shen
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Xiaoli Dong
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China.,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China
| | - Binghai Yan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, Israel
| | - Ziqiang Wang
- Department of Physics, Boston College, Chestnut Hill, MA, USA.
| | - Hong-Jun Gao
- Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China. .,School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, People's Republic of China. .,CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, People's Republic of China. .,Songshan Lake Materials Laboratory, Dongguan, People's Republic of China.
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9
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Liu X, Chong YX, Sharma R, Davis JCS. Atomic-scale visualization of electronic fluid flow. NATURE MATERIALS 2021; 20:1480-1484. [PMID: 34462570 DOI: 10.1038/s41563-021-01077-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Accepted: 07/12/2021] [Indexed: 06/13/2023]
Abstract
The most essential characteristic of any fluid is the velocity field, and this is particularly true for macroscopic quantum fluids1. Although rapid advances2-7 have occurred in quantum fluid velocity field imaging8, the velocity field of a charged superfluid-a superconductor-has never been visualized. Here we use superconducting-tip scanning tunnelling microscopy9-11 to image the electron-pair density and velocity fields of the flowing electron-pair fluid in superconducting NbSe2. Imaging of the velocity fields surrounding a quantized vortex12,13 finds electronic fluid flow with speeds reaching 10,000 km h-1. Together with independent imaging of the electron-pair density via Josephson tunnelling, we visualize the supercurrent density, which peaks above 3 × 107 A cm-2. The spatial patterns in electronic fluid flow and magneto-hydrodynamics reveal hexagonal structures coaligned to the crystal lattice and quasiparticle bound states14, as long anticipated15-18. These techniques pave the way for electronic fluid flow visualization studies of other charged quantum fluids.
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Affiliation(s)
- Xiaolong Liu
- Department of Physics, Cornell University, Ithaca, NY, USA
| | - Yi Xue Chong
- Department of Physics, Cornell University, Ithaca, NY, USA
| | - Rahul Sharma
- Department of Physics, Cornell University, Ithaca, NY, USA
- Department of Physics, University of Maryland, College Park, MD, USA
| | - J C Séamus Davis
- Department of Physics, Cornell University, Ithaca, NY, USA.
- Department of Physics, University College Cork, Cork, Ireland.
- Max-Planck Institute for Chemical Physics of Solids, Dresden, Germany.
- Clarendon Laboratory, University of Oxford, Oxford, UK.
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10
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Li Y, Zaki N, Garlea VO, Savici AT, Fobes D, Xu Z, Camino F, Petrovic C, Gu G, Johnson PD, Tranquada JM, Zaliznyak IA. Electronic properties of the bulk and surface states of Fe 1+yTe 1-xSe x. NATURE MATERIALS 2021; 20:1221-1227. [PMID: 33888904 DOI: 10.1038/s41563-021-00984-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 03/12/2021] [Indexed: 06/12/2023]
Abstract
The idea of employing non-Abelian statistics for error-free quantum computing ignited interest in reports of topological surface superconductivity and Majorana zero modes (MZMs) in FeTe0.55Se0.45. However, the topological features and superconducting properties are not observed uniformly across the sample surface. The understanding and practical control of these electronic inhomogeneities present a prominent challenge for potential applications. Here, we combine neutron scattering, scanning angle-resolved photoemission spectroscopy, and microprobe composition and resistivity measurements to characterize the electronic state of Fe1+yTe1-xSex. We establish a phase diagram in which the superconductivity is observed only at sufficiently low Fe concentration, in association with distinct antiferromagnetic correlations, whereas the coexisting topological surface state occurs only at sufficiently high Te concentration. We find that FeTe0.55Se0.45 is located very close to both phase boundaries, which explains the inhomogeneity of superconducting and topological states. Our results demonstrate the compositional control required for use of topological MZMs in practical applications.
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Affiliation(s)
- Yangmu Li
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
| | - Nader Zaki
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
| | - Vasile O Garlea
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - Andrei T Savici
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - David Fobes
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
| | - Zhijun Xu
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, USA
- Department of Materials Science and Engineering, University of Maryland, College Park, MD, USA
| | - Fernando Camino
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, USA
| | - Cedomir Petrovic
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
| | - Genda Gu
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
| | - Peter D Johnson
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
| | - John M Tranquada
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA
| | - Igor A Zaliznyak
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY, USA.
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11
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Fernández-Lomana M, Wu B, Martín-Vega F, Sánchez-Barquilla R, Álvarez-Montoya R, Castilla JM, Navarrete J, Marijuan JR, Herrera E, Suderow H, Guillamón I. Millikelvin scanning tunneling microscope at 20/22 T with a graphite enabled stick-slip approach and an energy resolution below 8 μeV: Application to conductance quantization at 20 T in single atom point contacts of Al and Au and to the charge density wave of 2H-NbSe 2. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:093701. [PMID: 34598511 DOI: 10.1063/5.0059394] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Accepted: 08/21/2021] [Indexed: 06/13/2023]
Abstract
We describe a scanning tunneling microscope (STM) that operates at magnetic fields up to 22 T and temperatures down to 80 mK. We discuss the design of the STM head, with an improved coarse approach, the vibration isolation system, and efforts to improve the energy resolution using compact filters for multiple lines. We measure the superconducting gap and Josephson effect in aluminum and show that we can resolve features in the density of states as small as 8 μeV. We measure the quantization of conductance in atomic size contacts and make atomic resolution and density of states images in the layered material 2H-NbSe2. The latter experiments are performed by continuously operating the STM at magnetic fields of 20 T in periods of several days without interruption.
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Affiliation(s)
- Marta Fernández-Lomana
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Beilun Wu
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Francisco Martín-Vega
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Raquel Sánchez-Barquilla
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Rafael Álvarez-Montoya
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - José María Castilla
- Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - José Navarrete
- SEGAINVEX, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | | | - Edwin Herrera
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Hermann Suderow
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Isabel Guillamón
- Laboratorio de Bajas Temperaturas y Altos Campos Magnéticos, Unidad Asociada (UAM/CSIC), Departamento de Física de la Materia Condensada, Instituto Nicolás Cabrera and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain
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12
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Liu X, Chong YX, Sharma R, Davis JCS. Discovery of a Cooper-pair density wave state in a transition-metal dichalcogenide. Science 2021. [DOI: 10.1126/science.abd4607] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Imaging an exotic state
Among the most intriguing of the many phases of cuprate superconductors is the so-called pair density wave (PDW) state. PDW is characterized by a spatially modulated density of Cooper pairs and can be detected with a scanning tunneling microscope equipped with a superconducting tip. Liu
et al.
used Josephson tunneling microscopy, modified for the task, to detect PDW in niobium diselenide, a superconductor with a layered hexagonal structure. The PDW state is expected to appear in other transition metal dichalcogenides as well.
Science
, abd4607, this issue p.
1447
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Affiliation(s)
- Xiaolong Liu
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14850, USA
| | - Yi Xue Chong
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14850, USA
| | - Rahul Sharma
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14850, USA
- Department of Physics, University of Maryland, College Park, MD 20740, USA
| | - J. C. Séamus Davis
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14850, USA
- Department of Physics, University College Cork, Cork T12 R5C, Ireland
- Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany
- Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, UK
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13
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Correlating Josephson supercurrents and Shiba states in quantum spins unconventionally coupled to superconductors. Nat Commun 2021; 12:1108. [PMID: 33597519 PMCID: PMC7889868 DOI: 10.1038/s41467-021-21347-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Accepted: 01/20/2021] [Indexed: 11/22/2022] Open
Abstract
Local spins coupled to superconductors give rise to several emerging phenomena directly linked to the competition between Cooper pair formation and magnetic exchange. These effects are generally scrutinized using a spectroscopic approach which relies on detecting the in-gap bound modes arising from Cooper pair breaking, the so-called Yu-Shiba-Rusinov (YSR) states. However, the impact of local magnetic impurities on the superconducting order parameter remains largely unexplored. Here, we use scanning Josephson spectroscopy to directly visualize the effect of magnetic perturbations on Cooper pair tunneling between superconducting electrodes at the atomic scale. By increasing the magnetic impurity orbital occupation by adding one electron at a time, we reveal the existence of a direct correlation between Josephson supercurrent suppression and YSR states. Moreover, in the metallic regime, we detect zero bias anomalies which break the existing framework based on competing Kondo and Cooper pair singlet formation mechanisms. Based on first-principle calculations, these results are rationalized in terms of unconventional spin-excitations induced by the finite magnetic anisotropy energy. Our findings have far reaching implications for phenomena that rely on the interplay between quantum spins and superconductivity. The impact of local magnetic impurities on superconducting order parameter remains largely unexplored. Here, the authors visualize the effect of different magnetic perturbations on a superconductor, unveiling a rich correlation of the interplay between quantum spins and superconductivity in different spectroscopic regimes.
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14
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Chatzopoulos D, Cho D, Bastiaans KM, Steffensen GO, Bouwmeester D, Akbari A, Gu G, Paaske J, Andersen BM, Allan MP. Spatially dispersing Yu-Shiba-Rusinov states in the unconventional superconductor FeTe 0.55Se 0.45. Nat Commun 2021; 12:298. [PMID: 33436594 PMCID: PMC7804303 DOI: 10.1038/s41467-020-20529-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 12/07/2020] [Indexed: 01/29/2023] Open
Abstract
By using scanning tunneling microscopy (STM) we find and characterize dispersive, energy-symmetric in-gap states in the iron-based superconductor FeTe0.55Se0.45, a material that exhibits signatures of topological superconductivity, and Majorana bound states at vortex cores or at impurity locations. We use a superconducting STM tip for enhanced energy resolution, which enables us to show that impurity states can be tuned through the Fermi level with varying tip-sample distance. We find that the impurity state is of the Yu-Shiba-Rusinov (YSR) type, and argue that the energy shift is caused by the low superfluid density in FeTe0.55Se0.45, which allows the electric field of the tip to slightly penetrate the sample. We model the newly introduced tip-gating scenario within the single-impurity Anderson model and find good agreement to the experimental data.
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Affiliation(s)
- Damianos Chatzopoulos
- grid.5132.50000 0001 2312 1970Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, Leiden, CA 2333 The Netherlands
| | - Doohee Cho
- grid.5132.50000 0001 2312 1970Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, Leiden, CA 2333 The Netherlands ,grid.15444.300000 0004 0470 5454Department of Physics, Yonsei University, Seoul, 03722 Republic of Korea
| | - Koen M. Bastiaans
- grid.5132.50000 0001 2312 1970Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, Leiden, CA 2333 The Netherlands
| | - Gorm O. Steffensen
- grid.5254.60000 0001 0674 042XCenter for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, Copenhagen Ø, 2100 Denmark
| | - Damian Bouwmeester
- grid.5132.50000 0001 2312 1970Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, Leiden, CA 2333 The Netherlands ,grid.5292.c0000 0001 2097 4740Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, Delft, CJ 2628 Netherlands
| | - Alireza Akbari
- grid.419507.e0000 0004 0491 351XMax Planck Institute for the Chemical Physics of Solids, Dresden, D-01187 Germany ,grid.49100.3c0000 0001 0742 4007Max Planck POSTECH Center for Complex Phase Materials, and Department of Physics, POSTECH, Pohang, Gyeongbuk 790-784 Korea
| | - Genda Gu
- grid.202665.50000 0001 2188 4229Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973 USA
| | - Jens Paaske
- grid.5254.60000 0001 0674 042XCenter for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, Copenhagen Ø, 2100 Denmark
| | - Brian M. Andersen
- grid.5254.60000 0001 0674 042XCenter for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, Copenhagen Ø, 2100 Denmark
| | - Milan P. Allan
- grid.5132.50000 0001 2312 1970Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, Leiden, CA 2333 The Netherlands
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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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Imaging the energy gap modulations of the cuprate pair-density-wave state. Nature 2020; 580:65-70. [PMID: 32238945 DOI: 10.1038/s41586-020-2143-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Accepted: 01/20/2020] [Indexed: 11/08/2022]
Abstract
The defining characteristic1,2 of Cooper pairs with finite centre-of-mass momentum is a spatially modulating superconducting energy gap Δ(r), where r is a position. Recently, this concept has been generalized to the pair-density-wave (PDW) state predicted to exist in copper oxides (cuprates)3,4. Although the signature of a cuprate PDW has been detected in Cooper-pair tunnelling5, the distinctive signature in single-electron tunnelling of a periodic Δ(r) modulation has not been observed. Here, using a spectroscopic technique based on scanning tunnelling microscopy, we find strong Δ(r) modulations in the canonical cuprate Bi2Sr2CaCu2O8+δ that have eight-unit-cell periodicity or wavevectors Q ≈ (2π/a0)(1/8, 0) and Q ≈ (2π/a0)(0, 1/8) (where a0 is the distance between neighbouring Cu atoms). Simultaneous imaging of the local density of states N(r, E) (where E is the energy) reveals electronic modulations with wavevectors Q and 2Q, as anticipated when the PDW coexists with superconductivity. Finally, by visualizing the topological defects in these N(r, E) density waves at 2Q, we find them to be concentrated in areas where the PDW spatial phase changes by π, as predicted by the theory of half-vortices in a PDW state6,7. Overall, this is a compelling demonstration, from multiple single-electron signatures, of a PDW state coexisting with superconductivity in Bi2Sr2CaCu2O8+δ.
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