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, we report a new approach for increasing the superconducting transition temperature ($T_{C}^{onset}$) 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 $T_{C}^{onset}$ of Fe(Te,Se) increases from nominally non-superconducting to as high as 12.5 K when $Bi_2Te_3$ is replaced with the topological phase $Bi_4Te_3$. Interfacing Fe(Te,Se) with $Bi_4Te_3$ is also found to be critical for stabilizing superconductivity in monolayer films where $T_{C}^{onset}$ can be as high as 6 K. Measurements of the electronic and crystalline structure of the $Bi_4Te_3$ 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.