Tracking Majorana Bound States in Superconductor-Topological Insulator-Superconductor Josephson junctions by transport measurements

Josephson junctions with a Superconductor-Topological Insulator-Superconductor (S-TI-S) geometry are expected to host Majorana Bound States (MBS) under certain conditions. In an external magnetic field, the MBS will be localized in Josephson vortices where the phase difference is an odd multiple of π. We describe and present progress on two experiments designed to test the interaction of pairs of Majorana states. In one experiment, we contrast the critical current diffraction patterns of two junction geometries - one geometry in which we proximitize only the top surface of the TI which creates localized MBS paired with delocalized Majorana extended states, with another geometry of junctions in which we proximitize both surfaces of the TI creating localized MBS pairs on the two surfaces. In the second experiment, we use a small field coil to apply a local magnetic field to the junction which tunes the distance between a pair of localized MBS. This can be detected as a modification of the critical current diffraction pattern and affects the hybridization of the Majorana states.