Pairing symmetry and capping layer influence of the superconductivity at FeSe/SrTiO₃interface

Single unit cell FeSe films on SrTiO₃ have attracted growing attention due to the enhancement of the superconducting critical temperature (T_c) over its bulk value and the possibility of topological superconductivity. The pairing symmetry and mechanisms underlying the superconducting gap have been studied via angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS). Here, we report the synthesis and characterization of ultrathin FeSe films grown on SrTiO₃ by molecular beam epitaxy. We gain insight into the symmetry of the gap by measuring the angular dependence of the in-plane critical magnetic field. Additionally, to understand the discrepancy between T_c measured by in-situ techniques (such as STS and ARPES) and ex-situ transport, we investigate how T_c is influenced by varying the capping layer and Fermi energy. Supported by the University of Chicago, the Vannevar Bush Fellowship, and 2DCC-MIP/NSF DMR-1539916.