Detection of a superconducting phase in a two-atom layer of hexagonal Ga   film grown on semiconducting GaN(0001)
  The recent observation of superconducting state at atomic scale has motivated the pursuit of exotic condensed phases in two-dimensional (2D) systems. Here we report on a superconducting phase in two-monolayer crystalline Ga films epitaxially grown on wide band-gap semiconductor GaN(0001). This phase exhibits a hexagonal structure and only 0.552 nm in thickness, nevertheless, brings about a superconducting transition temperature Tc as high as 5.4 K, confirmed by in situ scanning tunneling spectroscopy, and ex situ electrical magneto-transport and magnetization measurements. The anisotropy of critical magnetic field and Berezinski-Kosterlitz-Thouless-like transition are observed, typical for the 2D superconductivity. Our results demonstrate a novel platform for exploring atomic-scale 2D superconductor, with great potential for understanding of the interface superconductivity. 
Huimin Zhang, Yi Sun, Wei Li, Junping Peng, Can-Li Song, Ying Xing,   Qinghua Zhang, Jiaqi Guan, Zhi Li, Yanfei Zhao, Shuaih...
cond-mat.supr-con cond-mat.mes-hall