High T$_{\mathrm{C}}$ superconductivity in single-layer FeSe films on SrTiO$_3$*

The latest scanning tunneling spectroscopy and angle resolved photoemission spectroscopy of single-unit-cell FeSe films on SrTiO$_3$ show signatures of high temperature superconductivity with T$_{\mathrm{C}}$ \textgreater\ 55 K, the maximum value that has been stagnant since the discovery of the iron-based superconductors in 2008. Here we report a detailed transport study of the single-unit-cell FeSe film. Electrical transport measurements reveal a transition temperature of $\sim$ 50 K. The robust superconductivity is further confirmed by measuring Meissner effect. We show that the characteristics of the transition are consistent with a two-dimensional superconductor undergoing a Berezinskii-Kosterlitz-Thouless transition.