Supercurrents in a Topological Josephson Junction with a Magnetic Quantum Dot

Sammanfattning: The purpose of this master thesis is to investigate theoretically the influence of a nanomagnet on the Josephson effect displayed by phase biased point contacts consisting of topological superconductors. The device is modeled using the nonequilibrium Keldysh Green’s function technique. First, the Gor’kov Green’s functions are calculated. From these Green’s functions, the quasi-classical ones, relevant for energies around the Fermi energy, are obtained. Transport properties such as charge currents are calculated and analyzed in terms of the junction’s density of states displaying Andreev and Majorana states. The combination of the nanomagnet coupling and the spin-momentum locking of the topological superconductors generates a magneto-electric effect causing the supercurrent to depend strongly on the nanomagnet’s direction.