Signatures of Majorana Fermions in Hybrid Superconductor-Topological Insulator Josephson Junctions

We are studying the transport properties of lateral superconductor-topological insulator-superconductor Josephson junctions. In a magnetic field perpendicular to the TI surface, it is expected that localized zero-energy Majorana bound states will be stabilized in the junction at locations at which the phase difference is an odd-multiple of π, i.e. at the core of Josephson vortices. Our measurements of the critical current modulation patterns have shown lifting of odd nodes, which we interpret as evidence for a 4π-periodic sin(φ/2)-component in the Josephson current-phase relation (CPR), and motivated a model for the nucleation and manipulation of these Majorana states. In this talk, we summarize the results of a series of experiments designed to test in detail specific features of this model: (1) testing whether there is an even-odd pattern of node-lifting, (2) identifying irregular features in the diffraction pattern that could indicate the abrupt entry of Majorana states, (3) looking for changes in the noise distribution of critical currents that would indicate parity transitions of Majorana pairs, and (4) searching for non-sinusoidal components in direct measurements of the CPR using an asymmetric SQUID technique.