The superconductivity in single-layer FeTe$_{\mathrm{1-x}}$Se$_{\mathrm{x}}$ films on SrTiO$_{3}$

For bulk FeSe, the highest transition temperature \textit{Tc} $=$ 9 K has been observed for the composition with stoichiometry Fe$_{1.1}$Se. The tetragonal-orthorhombic structural transition observed in FeSe is suppressed with Te substitution and the superconducting transition temperature reaches a maximum of \textit{Tc} $=$15.2 K at about 50{\%} Te substitution. For single-layer FeSe films on SrTiO$_{3}$, \textit{ in situ} scanning tunneling microscopy and angle resolved photoemission spectroscopy have revealed a superconducting gap as large as 20 meV, and \textit{ex situ} transport measurements have confirmed the interface enhanced superconductivity with $T_{C}$ above 55 K. Here we report a detailed \textit{in situ} scanning tunneling microscopy and transport study of the single-layer FeTe$_{\mathrm{1-x}}$Se$_{\mathrm{x}}$ films on SrTiO$_{3}$. We found that Te substitution in the single-layer FeSe films doesn't induce further increase of the transition temperature \textit{Tc}, which is in contrast to the results for the corresponding bulk materials. This implies that the SrTiO$_{3}$ substrates play important role in the interfacial superconductivity.\\[4pt] [1] F. C. Hsu, \textit{et al.} Proc.Natl. Acad. Sci. U.S.A. \textbf{105} 14262 (2008).\\[0pt] [2] Y. Mizuguchi, \textit{et al.}, J. Phys. Soc. Jpn. \textbf{78} 074712 (2009).\\[0pt] [3] Q. Y. Wang \textit{et al.}, Chin Phys Lett, \textbf{29}, 037402 (2012).\\[0pt] [4] S. L. He, \textit{et al.} Nature Mater. \textbf{12,} 605 (2013).\\[0pt] [5] W. H. Zhang, \textit{et al.}, Chin Phys Lett, \textbf{31}, 017401 (2014).\\[0pt] [6] W. H. Zhang, \textit{et al.}, Phys. Rev. B \textbf{89}, 060506 (2014).