Electronic structure of high-T_c topological superconductor monolayer FeTe_1-xSe_x/SrTiO₃(001)

Topological superconductors are promising platforms for finding Majorana bound states, which are expected to be used in robust quantum computation. However, transition temperature of conventional superconductors is relatively low and single materials combined with high-temperature superconductivity (T_c) and topological nontrivial states are scarce in reality. Here, we performed angle-resolved photoemission spectroscopy studies on a series of FeTe_1-xSe_x monolayer films grown on SrTiO₃(STO). The superconductivity of the films is robust and rather insensitive to the variations of the band position. However, the band gap between the electron- and hole-like bands at the Brillouin zone center decreases towards band inversion and parity exchange, which drive the system to a nontrivial topological state predicted by theoretical calculations. Our results provide a clear experimental indication that the FeTe_1-xSe_x monolayer materials are high-temperature connate topological superconductors in which band topology and superconductivity are integrated intrinsically.