Topological Surface Superconductivity via Josephson Coupling in Bi₂Te₃/Nb

Since discoveries of protected conducting surface states, topological superconducting qubits have enchanted quantum science as prime elements in future fault-tolerant devices, particularly those based on Josephson junctions containing topological insulators. Still, Josephson coupling is often eclipsed by other proximity effects that can dilute topological superconducting pairing at the nontrivial insulator’s boundaries. Here, however, using an ultra-low-temperature scanning tunneling microscope, we detect Josephson physics in topological Bi₂Te₃films on superconducting Nb. At low temperatures, a previously undetected proximity gap varies little with Bi₂Te₃thickness and the density of states exhibits normal and superconducting components. Such observations are rationalized via Josephson pair tunneling through the (nearly) insulating Bi₂Te₃bulk, creating a rare, pure topological superconducting sheet. Our findings establish routes toward accessible topological superconducting states in qubits.