In situ electrical resistivity of FeSe thin films

Thin films of FeSe grown on SrTiO3 substrates have recently attracted great attention due to the dramatic superconducting Tc enhancement (70-100K) observed in monolayer films in comparison to bulk (9K). Despite substantial research efforts the transport evidence of superconductivity and its systematics remain difficult to obtain, as the extremely air-sensitive nature of these thin films precludes direct observation of superconductivity via traditional ex situ transport measurements without the addition of a potentially damaging capping layer. To circumvent this issue we construct an \textit{in situ} UHV four-point electrical contact probe in conjunction with angle-resolved photoemission spectroscopy to directly study the intrinsic macroscopic superconducting behavior of FeSe thin films. In particular, we investigate the thickness-dependence of the FeSe superconducting Tc as manifested in both transport and photoemission experiments.