Abstract
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The recent observation of the 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 twomonolayer
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 magnetotransport 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 superconductors,
with great potential for understanding the interface superconductivity