Scanning Tunneling Spectroscopy, Angle-resolved Photoemission Spectroscopy and Double-coil Mutual Inductance Investigation of Single Crystalline FeSe Superconductors*

We report investigation of single crystalline FeSe superconductors by combining scanning tunneling microscopy/spectroscopy (STM/S), angle-resolved photoemission spectroscopy (ARPES) and double-coil mutual inductance measurement, which were all applied in-situ to a sample cleaved in an ultra-high-vacuum (UHV) chamber. Using STM/S, we clearly observed the 1×1 atomic topography and the superconducting gap of this single crystal. In addition, ARPES was used to measure the band dispersion of FeSe. Finally, using a home built double-coil mutual inductance system, operating in UHV, we measured its superfluid density. These measurements shed light on the origin of superconductivity in FeSe. Additionally, using FeSe as a superconducting platform, we are investigating the proximity effect with other 2D materials.