Josephson current through a quantum dot coupled to a nanomagnet

Magnetically tunable nanoscale Josephson junctions have recently drawn increased attention since they offer interesting perspectives for superconducting spintronics. We theoretically study the transport through a junction consisting of two superconducting electrodes and a quantum dot which is coupled to a nanomagnet. A magnetic field applied to the central region lifts the spin degeneracy of the energy levels on the dot and starts a precession of the nanomagnet's magnetization with the Larmor frequency. This precession induces spin flips as well as a renormalization of the Zeeman splitting on the dot. The transport properties are calculated using a non-equilibrium Green's function approach. We show how the density of states on the dot is modified due to the nanomagnet and present the results for the current-phase relation. The current can be either suppressed or enhanced depending on the precession frequency, the coupling strength and the angle between the direction of the nanomagnet's magnetization and the magnetic field. Tuning the precession frequency can also cause the junction to undergo a 0 to π transition.