A Topological Superconductor Tuned by Electronic Correlation

Similar to other topological phases of matter, topological superconductivity can be profoundly tuned by electronic correlations through the modification of low-energy Fermiology, but not been elucidated so far. Here we uncover a unique topological superconducting phase in competition with electronic correlations in 10-unit-cell thick FeTe_xSe_1−x films grown on SrTiO₃ substrates. When the Te content x exceeds 0.7, we observe a rapid increase of the effective mass for the Fe d_xy band, with the emergence of a topological surface state and superconductivity; however, near the FeTe limit, the system enters an incoherent regime where the topological surface state becomes unidentifiable and superconductivity is suppressed. Dynamical mean field theory suggests that the electron-electron interactions in the odd-parity xy⁻ band with a strong d_xy character lead to an orbital-selective correlated phase, smearing out the topological electronic states and suppressing superconductivity. Our work establishes FeTe_xSe_1−x thin films as a unique platform distinct from the bulk counterpart. The substrate-induced strain suppresses the antiferromagnetism observed in bulk FeTe_xSe_1-x, and revamps the correlation-controlled topological superconductivity.