Novel Spin Dynamics in a Josephson Junction

The dynamics of a single spin embedded in the tunneling barrier between two superconductors was analzed. In order to analyze the time evolution of the spin, a generalized Wess Zumino Witten Novikov (WZWN) term was derived in the effective action for the spin on the Keldysh contours. It was found that the superconducting correlations led to an effective spin action which was nonlocal in time leading to unconventional precision. It was also found that the coupling of the spin to a superconducting bath produced nondamping spin retardation that resulted from additional nondissipative terms in the spin equations of motion.