title: Electronic evidence of an insulator-superconductor crossover in single-layer FeSe/SrTiO3 films.
abstract: In high-temperature cuprate superconductors, it is now generally agreed that superconductivity is realized by doping an antiferromagnetic Mott (charge transfer) insulator. The doping-induced insulator-to-superconductor transition has been widely observed in cuprates, which provides important information for understanding the superconductivity mechanism. In the iron-based superconductors, however, the parent compound is mostly antiferromagnetic bad metal, raising a debate on whether an appropriate starting point should go with an itinerant picture or a localized picture. No evidence of doping-induced insulator-superconductor transition (or crossover) has been reported in the iron-based compounds so far. Here, we report an electronic evidence of an insulator-superconductor crossover observed in the single-layer FeSe film grown on a SrTiO3 substrate. By taking angle-resolved photoemission measurements on the electronic structure and energy gap, we have identified a clear evolution of an insulator to a superconductor with increasing carrier concentration. In particular, the insulator-superconductor crossover in FeSe/SrTiO3 film exhibits similar behaviors to that observed in the cuprate superconductors. Our results suggest that the observed insulator-superconductor crossover may be associated with the two-dimensionality that enhances electron localization or correlation. The reduced dimensionality and the interfacial effect provide a new pathway in searching for new phenomena and novel superconductors with a high transition temperature.
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Junfeng
authors.initials: J
authors.lastname: He
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Xu
authors.initials: X
authors.lastname: Liu
authors.affiliation: State Key Lab of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China; Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Wenhao
authors.initials: W
authors.lastname: Zhang
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Lin
authors.initials: L
authors.lastname: Zhao
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Defa
authors.initials: D
authors.lastname: Liu
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Shaolong
authors.initials: S
authors.lastname: He
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Daixiang
authors.initials: D
authors.lastname: Mou
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Fangsen
authors.initials: F
authors.lastname: Li
authors.affiliation: State Key Lab of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China; Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Chenjia
authors.initials: C
authors.lastname: Tang
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Zhi
authors.initials: Z
authors.lastname: Li
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Lili
authors.initials: L
authors.lastname: Wang
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Yingying
authors.initials: Y
authors.lastname: Peng
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Chaoyu
authors.initials: C
authors.lastname: Chen
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Li
authors.initials: L
authors.lastname: Yu
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Guodong
authors.initials: G
authors.lastname: Liu
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Dong
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; and.
authors.forename: Chuangtian
authors.initials: C
authors.lastname: Chen
authors.affiliation: Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China; and.
authors.forename: Zuyan
authors.initials: Z
authors.lastname: Xu
authors.affiliation: State Key Lab of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China;
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; XJZhou@aphy.iphy.ac.cn qkxue@mail.tsinghua.edu.cn xcma@aphy.iphy.ac.cn.
authors.forename: Xucun
authors.initials: X
authors.lastname: Ma
authors.affiliation: State Key Lab of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China; XJZhou@aphy.iphy.ac.cn qkxue@mail.tsinghua.edu.cn xcma@aphy.iphy.ac.cn.
authors.forename: Qikun
authors.initials: Q
authors.lastname: Xue
authors.affiliation: National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; Collaborative Innovation Center of Quantum Matter, Beijing 100871, China XJZhou@aphy.iphy.ac.cn qkxue@mail.tsinghua.edu.cn xcma@aphy.iphy.ac.cn.
authors.forename: X J
authors.initials: XJ
authors.lastname: Zhou
keywords: ARPES; insulator-to-superconductor crossover; single-layer FeSe/SrTiO3 films