High-transparency topological-insulator-based Josephson junctions enabled by <i>in situ</i> low-temperature Al growth and wet etching

Abstract

Proximity-induced superconductivity in topological insulators (TIs) offers a promising platform for realizing Majorana zero modes (MZMs). However, disorder and interdiffusion at the superconductor/TI interface can substantially reduce the junction transparency, thereby suppressing the proximity effect and complicating the identification of MZMs. Here, we report high-transparency Al/(Bi1−xSbx)2Te3/Al Josephson junctions fabricated using in situ low-temperature growth of Al on (Bi1−xSbx)2Te3 thin films with x = 0.5. The resulting superconductor–normal-metal–superconductor (SNS) junctions exhibit robust supercurrent and clear features of multiple Andreev reflections. Excess-current analysis within the Octavio–Tinkham–Blonder–Klapwijk framework yields an effective interface transparency TJ ≈ 0.8. Quantum interference measurements show a SQUID-like pattern with non-vanishing critical current minima, while Dynes–Fulton inversion reveals enhanced supercurrent flow along the junction edges. This behavior is attributed to improved interface transparency at the edges, caused by reduced interfacial mixing near the edges during the device fabrication process.