Edge states and enhanced superconducting gaps in Bi islands on FeTe_0.55Se_0.45

By measuring scanning tunneling spectroscopy on some large Bi islands deposited on FeTe_0.55Se_0.45 superconductors, we observe clear in-gap edge states with double peaks at about ±1.0 meV on the spectra measured near the perimeter of the islands. This feature is very different from the single zero-energy peak observed on some other small Bi islands. The edge states spread towards the inner side of the islands over a width of 2-3 nm. The two edge-state peaks at positive and negative energies move to higher values with the increase of the magnetic field, and they disappear near the transition temperature of FeTe_0.55Se_0.45. Meanwhile, enhanced superconducting gaps are observed in the central regions of these Bi islands, which may be induced by the enhanced pair potential of the topological surface state. Our observations provide a valuable message for the edge state and the proximity-induced superconductivity on specific Bi islands grown on FeTe_0.55Se_0.45 substrate.