Real-space visualization of orbital-selective superconductivity in FeSe

Abstract

We investigate the orbitally resolved superconducting properties of bulk FeSe using scanning tunneling microscopy (STM). We find that the spectral weights of both the large $\Delta_1$ and small $\Delta_2$ superconducting gaps remain nearly unchanged at the top Se sites as the STM tip approaches atomic contact. In contrast, the spectral weight of $\Delta_2$ increases significantly at the Fe and bottom Se sites. These results suggest that the gap $\Delta_2$ is localized in the xy-plane and likely associated with the dxy orbital band. Furthermore, we observe a long-range suppression of the large gap $\Delta_1$ near one-dimensional (1D) defects such as twin boundaries, wrinkles, and step edges, whereas $\Delta_2$ remains robust. This indicates that the two superconducting gaps respond differently to such 1D defects. High-resolution measurement using a Pb-coated tip reveals localized in-gap states near 1D defects, indicating possible defect-induced magnetism. Our findings highlight the contrasting behaviors of gap $\Delta_1$ and gap $\Delta_2$ in response to local electronic and magnetic environments and provide real-space evidence for orbital-selective superconductivity.