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Ding C, Wei Z, Dong W, Feng H, Shi M, Wang L, Jia JF, Xue QK. Atomic-Site-Dependent Pairing Gap in Monolayer FeSe/SrTiO 3(001)-(√13 × √13). NANO LETTERS 2024; 24:8445-8452. [PMID: 38917425 DOI: 10.1021/acs.nanolett.4c02627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/27/2024]
Abstract
The interfacial FeSe/TiO2-δ coupling induces high-temperature superconductivity in monolayer FeSe films. Using cryogenic atomically resolved scanning tunneling microscopy/spectroscopy, we obtained atomic-site dependent surface density of states, work function, and the pairing gap in the monolayer FeSe on the SrTiO3(001)-(√13 × √13)-R33.7° surface. Our results disclosed the out-of-plane Se-Fe-Se triple layer gradient variation, switched DOS for Fe sites on and off TiO5□, and inequivalent Fe sublattices, which gives global spatial modulation of pairing gap contaminants with the (√13 × √13) pattern. Moreover, the coherent lattice coupling induces strong inversion asymmetry and in-plane anisotropy in the monolayer FeSe, which is demonstrated to correlate with the particle-hole asymmetry in coherence peaks. These results disclose delicate atomic-scale correlations between pairing and lattice-electronic coupling in the Bardeen-Cooper-Schrieffer to Bose-Einstein condensation crossover regime, providing insights into understanding the pairing mechanism of multiorbital superconductivity.
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Affiliation(s)
- Cui Ding
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area, Shenzhen 518045, China
| | - Zhongxu Wei
- Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
| | - Wenfeng Dong
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Hai Feng
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Mingxia Shi
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Lili Wang
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
| | - Jin-Feng Jia
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area, Shenzhen 518045, China
- Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
- Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Qi-Kun Xue
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area, Shenzhen 518045, China
- Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
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2
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Bahari M, Zhang SB, Li CA, Choi SJ, Rüßmann P, Timm C, Trauzettel B. Helical Topological Superconducting Pairing at Finite Excitation Energies. PHYSICAL REVIEW LETTERS 2024; 132:266201. [PMID: 38996321 DOI: 10.1103/physrevlett.132.266201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Revised: 04/19/2024] [Accepted: 05/15/2024] [Indexed: 07/14/2024]
Abstract
We propose helical topological superconductivity away from the Fermi surface in three-dimensional time-reversal-symmetric odd-parity multiband superconductors. In these systems, pairing between electrons originating from different bands is responsible for the corresponding topological phase transition. Consequently, a pair of helical topological Dirac surface states emerges at finite excitation energies. These helical Dirac surface states are tunable in energy by chemical potential and strength of band splitting. They are protected by time-reversal symmetry combined with crystalline twofold rotation symmetry. We suggest concrete materials in which this phenomenon could be observed.
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Affiliation(s)
| | | | - Chang-An Li
- Institute for Theoretical Physics and Astrophysics, University of Würzburg, D-97074 Würzburg, Germany
- Würzburg-Dresden Cluster of Excellence ct.qmat, Germany
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3
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Shi R, Li Q, Xu X, Han B, Zhu R, Liu F, Qi R, Zhang X, Du J, Chen J, Yu D, Zhu X, Guo J, Gao P. Atomic-scale observation of localized phonons at FeSe/SrTiO 3 interface. Nat Commun 2024; 15:3418. [PMID: 38653990 DOI: 10.1038/s41467-024-47688-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Accepted: 04/03/2024] [Indexed: 04/25/2024] Open
Abstract
In single unit-cell FeSe grown on SrTiO3, the superconductivity transition temperature features a significant enhancement. Local phonon modes at the interface associated with electron-phonon coupling may play an important role in the interface-induced enhancement. However, such phonon modes have eluded direct experimental observations. The complicated atomic structure of the interface brings challenges to obtain the accurate structure-phonon relation knowledge. Here, we achieve direct characterizations of atomic structure and phonon modes at the FeSe/SrTiO3 interface with atomically resolved imaging and electron energy loss spectroscopy in an electron microscope. We find several phonon modes highly localized (~1.3 nm) at the unique double layer Ti-O terminated interface, one of which (~ 83 meV) engages in strong interactions with the electrons in FeSe based on ab initio calculations. This finding of the localized interfacial phonon associated with strong electron-phonon coupling provides new insights into understanding the origin of superconductivity enhancement at the FeSe/SrTiO3 interface.
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Affiliation(s)
- Ruochen Shi
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871, China
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China
| | - Qize Li
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871, China
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China
- Department of Physics, University of California at Berkeley, Berkeley, CA, 94720, USA
| | - Xiaofeng Xu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Bo Han
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871, China
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China
| | - Ruixue Zhu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871, China
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China
| | - Fachen Liu
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, 100871, China
| | - Ruishi Qi
- Department of Physics, University of California at Berkeley, Berkeley, CA, 94720, USA
| | - Xiaowen Zhang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871, China
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China
| | - Jinlong Du
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China
| | - Ji Chen
- Institute of Condensed Matter and Material Physics, Frontiers Science Center for Nano-optoelectronics, School of Physics, Peking University, Beijing, 100871, China
- Collaborative Innovation Center of Quantum Matter, Beijing, 100871, China
- Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light-Element Advanced Materials, Peking University, Beijing, 100871, China
| | - Dapeng Yu
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China
- Shenzhen Institute for Quantum Science and Engineering (SIQSE), Southern University of Science and Technology, Shenzhen, 518055, China
- Hefei National Laboratory, 230088, Hefei, China
| | - Xuetao Zhu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
| | - Jiandong Guo
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
| | - Peng Gao
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, 100871, China.
- Electron Microscopy Laboratory, School of Physics, Peking University, Beijing, 100871, China.
- Collaborative Innovation Center of Quantum Matter, Beijing, 100871, China.
- Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light-Element Advanced Materials, Peking University, Beijing, 100871, China.
- Hefei National Laboratory, 230088, Hefei, China.
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Zhao D, Cui W, Liu Y, Gong G, Zhang L, Jia G, Zang Y, Hu X, Zhang D, Wang Y, Li W, Ji S, Wang L, He K, Ma X, Xue QK. Electronic inhomogeneity and phase fluctuation in one-unit-cell FeSe films. Nat Commun 2024; 15:3369. [PMID: 38643171 PMCID: PMC11032316 DOI: 10.1038/s41467-024-47350-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 03/25/2024] [Indexed: 04/22/2024] Open
Abstract
One-unit-cell FeSe films on SrTiO3 substrates are of great interest owing to significantly enlarged pairing gaps characterized by two coherence peaks at ±10 meV and ±20 meV. In-situ transport measurement is desired to reveal novel properties. Here, we performed in-situ microscale electrical transport and combined scanning tunneling microscopy measurements on continuous one-unit-cell FeSe films with twin boundaries. We observed two spatially coexisting superconducting phases in domains and on boundaries, characterized by distinct superconducting gaps (Δ 1 ~15 meV vs.Δ 2 ~10 meV) and pairing temperatures (Tp1~52.0 K vs. Tp2~37.3 K), and correspondingly two-step nonlinear V ~ I α behavior but a concurrent Berezinskii-Kosterlitz-Thouless (BKT)-like transition occurring atT BKT ~28.7 K. Moreover, the onset transition temperatureT c onset ~54 K and zero-resistivity temperatureT c zero ~31 K are consistent with Tp1 andT BKT , respectively. Our results indicate the broadened superconducting transition in FeSe/SrTiO3 is related to intrinsic electronic inhomogeneity due to distinct two-gap features and phase fluctuations of two-dimensional superconductivity.
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Affiliation(s)
- Dapeng Zhao
- Beijing Academy of Quantum Information Sciences, 100193, Beijing, China
| | - Wenqiang Cui
- Beijing Academy of Quantum Information Sciences, 100193, Beijing, China
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
| | - Yaowu Liu
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
| | - Guanming Gong
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
| | - Liguo Zhang
- Beijing Academy of Quantum Information Sciences, 100193, Beijing, China
| | - Guihao Jia
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
| | - Yunyi Zang
- Beijing Academy of Quantum Information Sciences, 100193, Beijing, China
| | - Xiaopeng Hu
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
| | - Ding Zhang
- Beijing Academy of Quantum Information Sciences, 100193, Beijing, China
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
- Frontier Science Center for Quantum Information, 100084, Beijing, China
| | - Yilin Wang
- School of Integrated Circuits, Shandong Technology Center of Nanodevices and Integration, State Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, China.
| | - Wei Li
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
- Frontier Science Center for Quantum Information, 100084, Beijing, China
| | - Shuaihua Ji
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
- Frontier Science Center for Quantum Information, 100084, Beijing, China
| | - Lili Wang
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China.
- Frontier Science Center for Quantum Information, 100084, Beijing, China.
| | - Ke He
- Beijing Academy of Quantum Information Sciences, 100193, Beijing, China
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
- Frontier Science Center for Quantum Information, 100084, Beijing, China
| | - Xucun Ma
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China
- Frontier Science Center for Quantum Information, 100084, Beijing, China
| | - Qi-Kun Xue
- Beijing Academy of Quantum Information Sciences, 100193, Beijing, China.
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, 100084, Beijing, China.
- Frontier Science Center for Quantum Information, 100084, Beijing, China.
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China.
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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. PHYSICAL REVIEW LETTERS 2023; 131:256002. [PMID: 38181352 DOI: 10.1103/physrevlett.131.256002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [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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Zakeri K, Rau D, Jandke J, Yang F, Wulfhekel W, Berthod C. Direct Probing of a Large Spin-Orbit Coupling in the FeSe Superconducting Monolayer on STO. ACS NANO 2023; 17:9575-9585. [PMID: 37155694 DOI: 10.1021/acsnano.3c02876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Spin-orbit coupling (SOC) is a fundamental physical interaction, which describes how the electrons' spin couples to their orbital motion. It is the source of a vast variety of fascinating phenomena in nanostructures. Although in most theoretical descriptions of high-temperature superconductivity SOC has been neglected, including this interaction can, in principle, revise the microscopic picture. Here by preforming energy-, momentum-, and spin-resolved spectroscopy experiments we demonstrate that while probing the dynamic charge response of the FeSe monolayer on strontium titanate, a prototype two-dimensional high-temperature superconductor using electrons, the scattering cross-section is spin dependent. We unravel the origin of the observed phenomenon and show that SOC in this two-dimensional superconductor is strong. We anticipate that such a strong SOC can have several consequences on the electronic structures and may compete with other pairing scenarios and be crucial for the mechanism of superconductivity.
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Affiliation(s)
- Khalil Zakeri
- Heisenberg Spin-dynamics Group, Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
| | - Dominik Rau
- Heisenberg Spin-dynamics Group, Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
| | - Jasmin Jandke
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
| | - Fang Yang
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
| | - Wulf Wulfhekel
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, Germany
- Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, D-76344, Eggenstein-Leopoldshafen, Germany
| | - Christophe Berthod
- Department of Quantum Matter Physics, University of Geneva, 1211 Geneva, Switzerland
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Stoichiometric Growth of Monolayer FeSe Superconducting Films Using a Selenium Cracking Source. CRYSTALS 2022. [DOI: 10.3390/cryst12060853] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [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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