Mapping the topological proximity-induced gap in multiterminal Josephson junctions

The energy of an Andreev bound state in a clean normal metal in contact with two superconductors disperses with the phase difference φ between superconducting leads similar to the energy of electrons in a 1D crystal lattice with quasimomentum k. A normal metal with n superconducting contacts maps onto a n-1 dimensional artificial crystal which has led to the proposal that multiterminal Josephson junctions (MTJJs) with n≥3 could host topological states [1]. In the devices studied here, topological nature of MTJJs manifests as a modulation of the quasiparticle density of states (DOS) in the normal metal that may be probed by tunneling measurements [2]. We show that one can reveal this modulation by measuring the resistance of diffusive MTJJs with normal contacts, which shows rich structure as a function of the phase differences φ_i [3]. Our approach demonstrates a simple yet powerful technique for exploring topological effects in MTJJs.

[1] Riwar, RP. et al. Nat Commun 7, 11167 (2016).

[2] Strambini, E. et al. Nature Nanotech 11, 1055–1059 (2016).

[3] Wisne, M. et al. Accepted, Phys. Rev. Lett. (2024) arXiv:2408.09023