Anisotropy of upper critical fields and interface superconductivity in FeSe/SrTiO3 grown by PLD

In this study, we grow FeSe/SrTiO${}_3$ with thicknesses of 4-19 nm using pulsed laser deposition and investigate their magneto-transport properties. The thinnest film (4 nm) exhibit negative Hall effect, indicating electron transfer into FeSe from the SrTiO${}_3$ substrate. This is in agreement with reports on ultrathin FeSe/SrTiO${}_3$ grown by molecular beam epitaxy. The upper critical field is found to exhibit large anisotropy ($\gamma >$ 11.9), estimated from the data near the transition temperature ($T_{\mathrm{c}}$). In particular, the estimated coherence lengths in the perpendicular direction are 0.15-0.27 nm, which are smaller than the c-axis length of FeSe, and are found to be almost independent of the total thicknesses of the films. These results indicate that superconductivity is confined at the interface of FeSe/SrTiO${}_3$.