Probing for topological signatures in phase-controlled multiterminal Josephson junctions

Andreev bound states in SNS junctions depend periodically on the Josephson phase φ between two superconductors, resembling the periodic dispersion of electron energy levels in a crystal lattice. A normal metal connected to n superconductors corresponds to a n-1 dimensional crystal. It has been predicted that the resulting “band structure” of such multiterminal Josephson junction devices may be topological [1]. In the case where the normal metal is diffusive, the quasiparticle density of states at the Fermi energy varies periodically with the phases, with gapped regions separated by regions where the gap completely closes. The dependence of the density of states can be probed by measuring the resistance of suitably designed diffusive devices [2]. We report on the fabrication and measurement of 3 terminal diffusive and ballistic devices, using a sample design that permits us to vary the two distinct phases independently.