4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions

TLDR

The Josephson effect generates a supercurrent across a weak link between superconductors, and recent work has explored coupling superconductors to the surface states of 3D topological insulators, where unconventional p‑wave superconductivity and 4π‑periodic gapless Andreev bound states are predicted. The study reports observing an anomalous rf response in a HgTe‑based Josephson junction and aims to enable further experiments probing induced superconductivity in 3D topological insulators. The anomalous rf response is attributed to a 4π‑periodic supercurrent component whose amplitude matches that expected from a gapless Andreev doublet.

Abstract

Abstract The Josephson effect describes the generic appearance of a supercurrent in a weak link between two superconductors. Its exact physical nature deeply influences the properties of the supercurrent. In recent years, considerable efforts have focused on the coupling of superconductors to the surface states of a three-dimensional topological insulator. In such a material, an unconventional induced p -wave superconductivity should occur, with a doublet of topologically protected gapless Andreev bound states, whose energies vary 4 π -periodically with the superconducting phase difference across the junction. In this article, we report the observation of an anomalous response to rf irradiation in a Josephson junction made of a HgTe weak link. The response is understood as due to a 4 π -periodic contribution to the supercurrent, and its amplitude is compatible with the expected contribution of a gapless Andreev doublet. Our work opens the way to more elaborate experiments to investigate the induced superconductivity in a three-dimensional insulator.