FeTe_1−xSe_x monolayer films: towards the realization of high-temperature connate topological superconductivity

We performed angle-resolved photoemission spectroscopy studies on a series of FeTe_1−xSe_x monolayer films grown on SrTiO₃. The superconductivity of the films is robust and rather insensitive to the variations of the band position and effective mass caused by the substitution of Se by Te. 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.