Proximity-effect-induced superconductivity in Bi2Te3/FeSe0.5Te0.5 thin-film heterostructures with different interface conditions

Proximity-effect-induced superconductivity is studied for high-quality ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}/\mathrm{Fe}{\mathrm{Se}}_{0.5}{\mathrm{Te}}_{0.5}$ (FST) thin-film heterostructures with atomically sharp interfaces and for ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}/{\mathrm{TiO}}_{2}$/FST heterostructures where ${\mathrm{TiO}}_{2}$ is the ultrathin buffer layer. Adjusting the buffer layer thickness from zero to several nanometers is used to simulate different interface conditions: strongly, weakly, and zero-coupled interfaces. It is found that, for the strongly coupled interface, both the ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ thin film and the FST have almost the same magnitude as the superconducting pair potential; for the weakly coupled interface, the pairing potential of the ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ thin film exhibits an approximately exponential decay with the ${\mathrm{TiO}}_{2}$ buffer layer thickness. Our experimental results can be explained qualitatively by several theories under different interface conditions.