Title: Tunable Fe-chalcogenide Heterostructures for Enhanced Superconductivity
Abstract: Fe-chalcogenides FeChs (Ch = S, Se, Te) have the simplest crystal structure among the different families of Fe-based superconductors. They share a common building block of a Fe square lattice tetrahedrally coordinated to chalcogen ions, where the Tc is controlled by the geometry of the edge-shared Fe(Ch)4 tetrahedron. Fe-chalcogenide films epitaxially grown on perovskite substrates offer a versatile platform for tuning the Ch-Fe-Ch tetrahedron angle towards achieving higher Tc. In this talk, I will present our studies of single-layer Fe-chalcogenide films grown by molecular beam epitaxy on SrTiO3(001) substrate, where we modify the Ch-Fe-Ch angle via UV light, chemical pressure, and substrate termination (SrO vs. TiO2). From comprehensive studies using in-situ STM/ARPES, ex-situ TEM imaging and x-ray scattering, and DFT/DMFT calculations, we show a strong correlation between the enhanced Tc and the Ch-Fe-Ch angle in these single-layer films. I will also highlight our observation of Tomonaga-Luttinger liquid behavior in the topological edge channels in multilayer FeSe films and its tunability by chemical pressure. These findings indicate that epitaxial Fe-chalcogenide heterostructures are a highly tunable quantum system and shed light on the Cooper pairing and topological properties of Fe-chalcogenide superconductors.