The inverse proximity effect between topological insulator Bi2Te3 and superconductor NbTiN

Inducing a superconducting gap in topological materials via the proximity effect has been a widely applied approach to exploring topological superconductivity. However, the inverse proximity effect, which can provide crucial insights for understanding topological insulator-superconductor (TI-SC) Josephson junctions, remains largely unexplored thus far. In this study, we report the successful epitaxy of a TI-SC heterostructure using NbTiN as the superconductor layer and investigate the inverse proximity effect in it. Electrical transport measurements reveal a systematic suppression of the superconducting transition temperature with increasing Bi2Te3 thickness, reaching ∼23% in the 10 nm NbTiN samples and tending toward saturation at larger Bi2Te3 thickness. This behavior resembles the inverse proximity effect in conventional superconductor-normal metal bilayers. The perpendicular upper critical field yields a coherence length with only weak thickness dependence. Angle-resolved photoemission spectroscopy resolves the Bi2Te3 Dirac surface state and shows no detectable thickness-dependent shift of the Dirac point. Our results establish a model system to investigate the inverse proximity effect in TI-SC heterostructures with sharp superconducting transitions at ultrathin thickness, offering important insights into a deep understanding of TI-SC Josephson junctions.