University of Cologne Uncovers Spectroscopic Evidence of Topological Superconductivity in TI Josephson Junctions
AI-summarised brief · reviewed before publication
Physicists at the University of Cologne, together with theorists from RWTH Aachen, performed tunneling spectroscopy on BiSbTeSe₂‑based topological‑insulator Josephson junctions and observed a phase‑controlled closing and reopening of the induced superconducting gap. The experiment, published in Science Advances, provides the first local spectroscopic confirmation of the 2008 Fu‑Kane model, demonstrating that Majorana‑compatible zero‑energy modes can appear without applying destructive Zeeman fields. By embedding a 50 nm planar junction in an RF‑SQUID loop, the team varied the superconducting phase φ with out‑of‑plane flux and recorded a 130 µeV gap at φ = 0 that vanished near φ = π, producing a zero‑bias feature. Dual tunnel probes tracked vortex‑induced phase periodicities, confirming localization of zero‑energy states at phase gradients. The authors note that the current energy resolution (≈30 µeV) limits proof of a truly gapless transition and propose using niobium electrodes and charge‑sensing electrometry to achieve the 4π‑periodic parity flips required for topological qubits.
💡 Why It Matters
- · Demonstrating phase‑tuned gap closure without magnetic fields offers a cleaner route to Majorana modes, sidestepping the false‑positive signals that have plagued nanowire approaches.
