Phase Diagram and High Temperature Superconductivity at 65 K in Tuning   Carrier Concentration of Single-Layer FeSe Films
  Superconductivity in the cuprate superconductors and the Fe-based superconductors is realized by doping the parent compound with charge carriers, or by application of high pressure, to suppress the antiferromagnetic state. Such a rich phase diagram is important in understanding superconductivity mechanism and other physics in the Cu- and Fe-based high temperature superconductors. In this paper, we report a phase diagram in the single-layer FeSe films grown on SrTiO3 substrate by an annealing procedure to tune the charge carrier concentration over a wide range. A dramatic change of the band structure and Fermi surface is observed, with two distinct phases identified that are competing during the annealing process. Superconductivity with a record high transition temperature (Tc) at ~65 K is realized by optimizing the annealing process. The wide tunability of the system across different phases, and its high-Tc, make the single-layer FeSe film ideal not only to investigate the superconductivity physics and mechanism, but also to study novel quantum phenomena and for potential applications. 
Shaolong He, Junfeng He, Wenhao Zhang, Lin Zhao, Defa Liu, Xu Liu,   Daixiang Mou, Yun-Bo Ou, Qing-Yan Wang, Zhi Li, Lili Wa...
cond-mat.supr-con cond-mat.mtrl-sci cond-mat.str-el