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Xue CL, Dou LG, Xu YJ, Yuan QQ, Li QY, Jia ZY, Li Z, Liu R, Li SC. Iron Vacancy Tunable Superconductor-Insulator Transition in FeSe/SrTiO_{3} Monolayer. Phys Rev Lett 2023; 131:256002. [PMID: 38181352 DOI: 10.1103/physrevlett.131.256002] [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: 04/05/2023] [Revised: 11/15/2023] [Accepted: 11/21/2023] [Indexed: 01/07/2024]
Abstract
The Fe_{4}Se_{5} with a sqrt[5]×sqrt[5] Fe vacancy order is suggested to be a Mott insulator and the parent state of bulk FeSe superconductor. The iron vacancy ordered state has been considered as a Mott insulator and the parent compound of bulk FeSe-based superconductors. However, for the superconducting FeSe/SrTiO_{3} monolayer (FeSe/STO) with an interface-enhanced high transition temperature (T_{c}), the electronic evolution from its Fe vacancy ordered parent phase to the superconducting state, has not been explored due to the challenge to realize an Fe vacancy order in the FeSe/STO monolayer, even though important to the understanding of superconductivity mechanism. In this study, we developed a new method to generate Fe vacancies within the FeSe/STO monolayer in a tunable fashion, with the assistance of atomic hydrogen. As a consequence, an insulating sqrt[5]×sqrt[5] Fe vacancy ordered monolayer is realized as the parent state. By using scanning tunneling microscopy and scanning tunneling spectroscopy, the spectral evolution from superconductivity to insulator is fully characterized. Surprisingly, a prominent spectral weight transfer occurs, thus implying a strong electron correlation effect. Moreover, the Fe vacancy induced insulating gap exhibits no Mott gap-like features. This work provides new insights in understanding the high-T_{c} superconductivity in FeSe/STO monolayer.
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Affiliation(s)
- Cheng-Long Xue
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
| | - Li-Guo Dou
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
| | - Yong-Jie Xu
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
| | - Qian-Qian Yuan
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
| | - Qi-Yuan Li
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
| | - Zhen-Yu Jia
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
| | - Zishuang Li
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
| | - Ronghua Liu
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
- Jiangsu Provincial Key Laboratory for Nanotechnology, Nanjing University, Nanjing 210093, China
| | - Shao-Chun Li
- National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
- Jiangsu Provincial Key Laboratory for Nanotechnology, Nanjing University, Nanjing 210093, China
- Hefei National Laboratory, Hefei 230088, China
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Wei Z, Qin S, Ding C, Wu X, Hu J, Sun YJ, Wang L, Xue QK. Identifying s-wave pairing symmetry in single-layer FeSe from topologically trivial edge states. Nat Commun 2023; 14:5302. [PMID: 37652936 PMCID: PMC10471577 DOI: 10.1038/s41467-023-40931-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 08/11/2023] [Indexed: 09/02/2023] Open
Abstract
Determining the pairing symmetry of single-layer FeSe on SrTiO3 is the key to understanding the enhanced pairing mechanism. It also guides the search for superconductors with high transition temperatures. Despite considerable efforts, it remains controversial whether the symmetry is the sign-preserving s- or the sign-changing s±-wave. Here, we investigate the pairing symmetry of single-layer FeSe from a topological point of view. Using low-temperature scanning tunneling microscopy/spectroscopy, we systematically characterize the superconducting states at edges and corners of single-layer FeSe. The tunneling spectra collected at edges and corners show a full energy gap and a substantial dip, respectively, suggesting the absence of topologically non-trivial edge and corner modes. According to our theoretical calculations, these spectroscopic features can be considered as strong evidence for the sign-preserving s-wave pairing in single-layer FeSe.
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Affiliation(s)
- Zhongxu Wei
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, China
| | - Shengshan Qin
- School of Physics, Beijing Institute of Technology, Beijing, 100081, China
- Kavli Institute of Theoretical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Cui Ding
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, China
- Beijing Academy of Quantum Information Sciences, Beijing, 100193, China
| | - Xianxin Wu
- CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Jiangping Hu
- Kavli Institute of Theoretical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100049, China
- Beijing National Research Center for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Yu-Jie Sun
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China.
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen, 518045, China.
| | - Lili Wang
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, China.
| | - Qi-Kun Xue
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China.
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, China.
- Beijing Academy of Quantum Information Sciences, Beijing, 100193, China.
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen, 518045, China.
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Zou Q, Oli BD, Zhang H, Benigno J, Li X, Li L. Deciphering Alloy Composition in Superconducting Single-Layer FeSe 1-xS x on SrTiO 3(001) Substrates by Machine Learning of STM/S Data. ACS Appl Mater Interfaces 2023; 15:22644-22650. [PMID: 37125966 PMCID: PMC10176460 DOI: 10.1021/acsami.2c23324] [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: 05/11/2023]
Abstract
Scanning tunneling microscopy (STM) is a powerful technique for imaging atomic structure and inferring information on local elemental composition, chemical bonding, and electronic excitations. However, a plain visual analysis of STM images can be challenging for such determination in multicomponent alloys, particularly beyond the diluted limit due to chemical disorder and electronic inhomogeneity. One viable solution is to use machine learning to analyze STM data and identify hidden patterns and correlations. Here, we apply this approach to determine the Se/S concentration in superconducting single-layer FeSe1-xSx alloys epitaxially grown on SrTiO3(001) substrates via molecular beam epitaxy. First, the K-means clustering method is applied to identify defect-related dI/dV tunneling spectra taken by current imaging tunneling spectroscopy. Then, the Se/S ratio is calculated by analyzing the remaining spectra based on the singular value decomposition method. Such analysis provides an efficient and reliable determination of alloy composition and further reveals the correlations of nanoscale chemical inhomogeneity to superconductivity in single-layer iron chalcogenide films.
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Affiliation(s)
- Qiang Zou
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Basu Dev Oli
- 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
| | - Joseph Benigno
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Xin Li
- Lane Department of Computer Science and Electrical Engineering, 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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Zhu K, Wang H, Zhu Y, Zang Y, Feng Y, Tong B, Zhao D, Xie X, Chang K, He K, Liu C. Stoichiometric Growth of Monolayer FeSe Superconducting Films Using a Selenium Cracking Source. Crystals 2022; 12:853. [DOI: 10.3390/cryst12060853] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
As a novel interfacial high-temperature superconductor, monolayer FeSe on SrTiO3 has been intensely studied in the past decade. The high selenium flux involved in the traditional growth method complicates the film’s composition and entails more sample processing to realize the superconductivity. Here we use a Se cracking source for the molecular beam epitaxy growth of FeSe films to boost the reactivity of the Se flux. Reflection high-energy electron diffraction shows that the growth rate of FeSe increases with the increasing Se flux when the Fe flux is fixed, indicating that the Se over-flux induces Fe vacancies. Through careful tuning, we find that the proper Se/Fe flux ratio with Se cracked that is required for growing stoichiometric FeSe is close to 1, much lower than that with the uncracked Se flux. Furthermore, the FeSe film produced by the optimized conditions shows high-temperature superconductivity in the transport measurements without any post-growth treatment. Our work reinforces the importance of stoichiometry for superconductivity and establishes a simpler and more efficient approach to fabricating monolayer FeSe superconducting films.
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Xie J, Liu X, Zhang W, Wong SM, Zhou X, Zhao Y, Wang S, Lai KT, Goh SK. Fragile Pressure-Induced Magnetism in FeSe Superconductors with a Thickness Reduction. Nano Lett 2021; 21:9310-9317. [PMID: 34714653 DOI: 10.1021/acs.nanolett.1c03508] [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] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The emergence of high transition temperature (Tc) superconductivity in bulk FeSe under pressure is associated with the tuning of nematicity and magnetism. However, sorting out the relative contributions from magnetic and nematic fluctuations to the enhancement of Tc remains challenging. Here, we design and conduct a series of high-pressure experiments on FeSe thin flakes. We find that as the thickness decreases the nematic phase boundary on temperature-pressure phase diagrams remains robust while the magnetic order is significantly weakened. A local maximum of Tc is observed outside the nematic phase region, not far from the extrapolated nematic end point in all samples. However, the maximum Tc value is reduced associated with the weakening of magnetism. No high-Tc phase is observed in the thinnest sample. Our results strongly suggest that nematic fluctuations alone can only have a limited effect while magnetic fluctuations are pivotal on the enhancement of Tc in FeSe.
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Affiliation(s)
- Jianyu Xie
- Department of Physics, The Chinese University of Hong Kong, Hong Kong SAR, China
| | - Xinyou Liu
- Department of Physics, The Chinese University of Hong Kong, Hong Kong SAR, China
| | - Wei Zhang
- Department of Physics, The Chinese University of Hong Kong, Hong Kong SAR, China
| | - Sum Ming Wong
- Department of Physics, The Chinese University of Hong Kong, Hong Kong SAR, China
| | - Xuefeng Zhou
- Department of Physics, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China
| | - Yusheng Zhao
- Department of Physics, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China
| | - Shanmin Wang
- Department of Physics, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China
| | - Kwing To Lai
- Department of Physics, The Chinese University of Hong Kong, Hong Kong SAR, China
| | - Swee K Goh
- Department of Physics, The Chinese University of Hong Kong, Hong Kong SAR, China
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6
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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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7
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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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8
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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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Ge Z, Zou Q, Zhang H, Yan C, Agterberg D, Weinert M, Li L. Superconductivity on Edge: Evidence of a One-Dimensional Superconducting Channel at the Edges of Single-Layer FeTeSe Antiferromagnetic Nanoribbons. ACS Nano 2020; 14:6539-6547. [PMID: 32363855 DOI: 10.1021/acsnano.9b08726] [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: 06/11/2023]
Abstract
How superconductivity emerges from antiferromagnetic ordering is an essential question for Fe-based superconductors. Here, we explore the effect of dimensionality on the interplay between antiferromagnetic ordering and superconductivity by investigating nanoribbons of single-layer FeTe1-xSex films grown on SrTiO3(001) substrates by molecular beam epitaxy. Using scanning tunneling microscopy/spectroscopy, we find a one-dimensional (1D) superconducting channel 2 nm wide with a TC of 42 ± 4 K on the edge of FeTe1-xSex (x < 0.1) ribbons, coexisting with a non-superconducting ribbon interior that remains bicollinear antiferromagnetically ordered. Density functional theory calculations indicate that both Se and the presence of the edge destabilize the bicollinear antiferromagnetic magnetic order, resulting in a paramagnetic region near the edge with strong local checkerboard fluctuations that is conducive to superconductivity. Our results represent the highest TC achieved in 1D superconductors and demonstrate an effective route toward stabilizing superconductivity in Fe-based superconductors at reduced dimensions.
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Affiliation(s)
- Zhuozhi Ge
- 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
| | - Huimin Zhang
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Chenhui Yan
- 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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Song SY, Martiny JHJ, Kreisel A, Andersen BM, Seo J. Visualization of Local Magnetic Moments Emerging from Impurities in Hund's Metal States of FeSe. Phys Rev Lett 2020; 124:117001. [PMID: 32242691 DOI: 10.1103/physrevlett.124.117001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 09/30/2019] [Accepted: 02/21/2020] [Indexed: 06/11/2023]
Abstract
Understanding the origin of the magnetism of high temperature superconductors is crucial for establishing their unconventional pairing mechanism. Recently, theory predicts that FeSe is close to a magnetic quantum critical point, and thus weak perturbations such as impurities could induce local magnetic moments. To elucidate such quantum instability, we have employed scanning tunneling microscopy and spectroscopy. In particular, we have grown FeSe film on superconducting Pb(111) using molecular beam epitaxy and investigated magnetic excitation caused by impurities in the proximity-induced superconducting gap of FeSe. Our study provides deep insight into the origin of the magnetic ordering of FeSe by showing the way local magnetic moments develop in response to impurities near the magnetic quantum critical point.
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Affiliation(s)
- Sang Yong Song
- Department of Emerging Materials Science, DGIST, 333 Techno-Jungang-daero, Hyeonpung-Eup, Dalseong-Gun, Daegu 42988, Korea
| | - J H J Martiny
- Center for Nanostructured Graphene (CNG), Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - A Kreisel
- Institut für Theoretische Physik, Universität Leipzig, D-04103 Leipzig, Germany
| | - B M Andersen
- Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, DK-2100 Copenhagen, Denmark
| | - Jungpil Seo
- Department of Emerging Materials Science, DGIST, 333 Techno-Jungang-daero, Hyeonpung-Eup, Dalseong-Gun, Daegu 42988, Korea
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Yao G, Duan MC, Liu N, Wu Y, Guan DD, Wang S, Zheng H, Li YY, Liu C, Jia JF. Diamagnetic Response of Potassium-Adsorbed Multilayer FeSe Film. Phys Rev Lett 2019; 123:257001. [PMID: 31922797 DOI: 10.1103/physrevlett.123.257001] [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: 04/08/2019] [Revised: 07/23/2019] [Indexed: 06/10/2023]
Abstract
Intrigued by the discovery of high-temperature superconductivity in a single unit-cell layer of FeSe film on SrTiO_{3}, researchers recently found large superconductinglike energy gaps in K-adsorbed multilayer FeSe films by angle-resolved photoemission and scanning tunneling spectroscopy. However, the existence and nature of the high-temperature superconductivity inferred by the spectroscopic studies has not been investigated by measurements of zero resistance or the Meissner effect due to the fragility of K atoms in air. Using a self-developed multifunctional scanning tunneling microscope, we succeed in observing the diamagnetic response of K-adsorbed multilayer FeSe films, and thus find a dome-shaped relation between the critical temperature (T_{c}) and K coverage. Intriguingly, T_{c} exhibits an approximately linear dependence on the superfluid density in the whole K adsorbed region. Moreover, the quadratic low-temperature variation in the London penetration depth indicates a sign-reversal order parameter. These results provide compelling information towards further understanding of the high-temperature superconductivity in FeSe-derived superconductors.
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Affiliation(s)
- Gang Yao
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Ming-Chao Duan
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Ningning Liu
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Yanfu Wu
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Dan-Dan Guan
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Shiyong Wang
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Hao Zheng
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Yao-Yi Li
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - Canhua Liu
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
- Tsung-Dao Lee Institute, Shanghai 200240, China
| | - Jin-Feng Jia
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
- Tsung-Dao Lee Institute, Shanghai 200240, China
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