Interfacially Enhanced Superconductivity in Fe(Te,Se)/Bi4Te3 Heterostructures

Realizing topological superconductivity by integrating high-transition-temperature (T_C) superconductors with topological insulators can open new paths for quantum computing applications. Here, a new approach is reported for increasing the superconducting transition temperature $\left(T_C^{\mathrm{onset}}\right)$ by interfacing the unconventional superconductor Fe(Te,Se) with the topological insulator Bi–Te system in the low-Se doping regime, near where superconductivity vanishes in the bulk. The critical finding is that the $T_C^{\mathrm{onset}}$ of Fe(Te,Se) increases from nominally non-superconducting to as high as 12.5 K when Bi₂Te₃ is replaced with the topological phase Bi₄Te₃. Interfacing Fe(Te,Se) with Bi₄Te₃ is also found to be critical for stabilizing superconductivity in monolayer films where $T_C^{\mathrm{onset}}$ can be as high as 6 K. Measurements of the electronic and crystalline structure of the Bi₄Te₃ layer reveal that a large electron transfer, epitaxial strain, and novel chemical reduction processes are critical factors for the enhancement of superconductivity. This novel route for enhancing T_C in an important epitaxial system provides new insight on the nature of interfacial superconductivity and a platform to identify and utilize new electronic phases.