Single layer FeSe film grown on SrTiO3 substrate has drawn much interest for its novel interfacial effects, which have led to the highest superconducting temperature (TC) to date amongst all Fe-based superconductors. While several paring symmetries, such as s++-wave, nodeless d-wave, as well as s+/--wave have been suggested, the experimental determination of its superconducting paring symmetry remains elusive. Here we investigate the intrinsic impurity-induced in-gap bound states and quasiparticle interference (QPI) patterns in single layer FeSe/SrTiO3 by scanning tunneling microscopy/spectroscopy. We observed bound states induced by nonmagnetic impurities, which strongly suggests a sign-changing order parameter. Through detailed analysis of the phase-sensitive QPI patterns, we further confirm that the order parameter indeed changes sign within the electron pockets. This identification of a sign change pairing symmetry in single layer FeSe/SrTiO3 presents an important step towards the understanding of the mechanism of its high Tc superconductivity.This research is supported by DOE (DE-SC0017632).
APS March Meeting Abstracts
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