title: Tuning Superconductivity in FeSe Thin Films via Magnesium Doping.
abstract: In contrast to its bulk crystal, the FeSe thin film or layer exhibits better superconductivity performance, which recently attracted much interest in its fundamental research as well as in potential applications around the world. In the present work, tuning superconductivity in FeSe thin films was achieved by magnesium-doping technique. Tc is significantly enhanced from 10.7 K in pure FeSe films to 13.4 K in optimized Mg-doped ones, which is approximately 1.5 times higher than that of bulk crystals. This is the first time achieving the enhancement of superconducting transition temperature in FeSe thin films with practical thickness (120 nm) via a simple Mg-doping process. Moreover, these Mg-doped FeSe films are quite stable in atmosphere with Hc2 up to 32.7 T and Tc(zero) up to 12 K, respectively, implying their outstanding potential for practical applications in high magnetic fields. It was found that Mg enters the matrix of FeSe lattice, and does not react with FeSe forming any other secondary phase. Actually, Mg first occupies Fe-vacancies, and then substitutes for some Fe in the FeSe crystal lattices when Fe-vacancies are fully filled. Simultaneously, external Mg-doping introduces sufficient electron doping and induces the variation of electron carrier concentration according to Hall coefficient measurements. This is responsible for the evolution of superconducting performance in FeSe thin films. Our results provide a new strategy to improve the superconductivity of 11 type Fe-based superconductors and will help us to understand the intrinsic mechanism of this unconventional superconducting system.
authors.affiliation: Institute for Superconducting and Electronic Materials, AIIM, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia.|Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, Shanghai University , Shanghai 200444, People's Republic of China.
authors.forename: Wenbin
authors.initials: W
authors.lastname: Qiu
authors.affiliation: Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science & Engineering, Tianjin University , Tianjin 300072, People's Republic of China.|Institute for Superconducting and Electronic Materials, AIIM, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia.
authors.forename: Zongqing
authors.initials: Z
authors.lastname: Ma
authors.affiliation: Tianjin Key Laboratory of Composite and Functional Materials, School of Materials Science & Engineering, Tianjin University , Tianjin 300072, People's Republic of China.
authors.forename: Yongchang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Institute for Superconducting and Electronic Materials, AIIM, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Shahriar Al Hossain
authors.affiliation: Institute for Superconducting and Electronic Materials, AIIM, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Wang
authors.affiliation: Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, Shanghai University , Shanghai 200444, People's Republic of China.
authors.forename: Chuanbing
authors.initials: C
authors.lastname: Cai
authors.affiliation: Institute for Superconducting and Electronic Materials, AIIM, University of Wollongong , Squires Way, North Wollongong, New South Wales 2500, Australia.
authors.forename: Shi Xue
authors.initials: SX
authors.lastname: Dou
keywords: FeSe film; Mg-doping; electron concentration; pulsed laser deposition; superconductivity