Interface-induced high-temperature superconductivity in FeSe/TiO$_2$(001) heterostructure

The recently discovered high transition temperature ($T_c$) superconductivity at the interface of single unit-cell (UC) FeSe films on SrTiO$_3$(001) has generated considerable excitement [1,2], which may eventually lead to the discovery of a new family of high-$T_c$ superconductors at many different interfaces. In this talk, we will present our recent work on a new interfacial system with high-$T_c$ superconductivity, 1 UC FeSe films on anatase TiO$_2$(001). By using molecular beam epitaxy (MBE) techniques, we have successfully prepared high-quality 1 UC FeSe films on anatase TiO$_2$(001) formed on SrTiO$_3$. \textit{In situ} scanning tunneling spectroscopy (STS) reveals large superconducting gap ($\Delta$) ranging from 17 meV to 22 meV, which is nearly one order of magnitude larger than $\Delta$ = 2.2 meV of bulk FeSe with $T_c$ = 9.4 K, indicating the signature of high-$T_c$ superconductivity. The superconductivity of this heterostructure system is further verified by imaging vortex lattice under external magnetic field. By examining the distinct properties of anatase TiO$_2$ from SrTiO$_3$, as well as their influences on superconductivity, we will also discuss about the possible pairing mechanism of this system. Together with our previous work of 1 UC FeSe/SrTiO$_3$ [1,2], this work demonstrates that interface engineering is a powerful way to fabricate new high-$T_c$ superconductors and investigate the mechanism of high-$T_c$ superconductivity.\\[4pt] [1] Q.-Y. Wang \textit{et al.}, \textit{Chin. Phys. Lett.} \textbf{29,} 037402 (2012).\\[0pt] [2] W.-H. Zhang \textit{et al.}, \textit{Chin. Phys. Lett.} \textbf{31,} 017401 (2014).