Tunneling spectroscopy and Josephson current of superconductor-ferromagnet hybrids on the surface of a 3D TI

We investigate the charge transport property of superconductor (S)/normal metal (N)/ ferromagnet insulator (FI)/(normal metal) N' and S/N/FI/N'/S Josephson junctions on a three-dimensional topological insulator surface. We find the asymmetric local density of states (LDOSs) in a S/N/FI/N' junction and show that the N interlayer gives rise to subgap resonant spikes in the differential conductance and LDOSs. In a S/N/FI/N'/S junction, the Josephson current shows a non-sinusoidal current-phase relation and the N (or N') interlayer decreases the magnitude of the critical current monotonically. (paper)