Spin and current variations in Josephson junctions
A. Shnirman1, Z. Nussinov2, Jian-Xin Zhu2, A.V. Balatsky2, and Yu. Makhlin1,3
1Institut für Theoretische Festkörperphysik, Universität Karlsruhe, D-76128 Karlsruhe, Germany 2Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
3Landau Institute for Theoretical Physics, Kosygin Str. 2, 117940 Moscow, Russia
Received February 2, 2004
We study the dynamics of a single spin embedded in the tunneling barrier between two superconductors.
As a consequence of pair correlations in the superconducting state, the spin displays rich and unusual dynamics. To properly describe the time evolution of the spin we derive the effective Keldysh action for the spin. The superconducting correlations lead to an effective spin action, which is nonlocal in time, leading to unconventional precession. We further illustrate how the current is modulated by this novel spin dynamics.PACS: 74.50.+r - Tunneling phenomena; point contacts, weak links, Josephson effects (for SQUIDs, see 85.25.Dq; for Josephson devices, see 85.25.Cp; for Josephson junction arrays, see 74.81.Fa) 75.20.Hr - Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions (see also 72.15.Qm Scattering mechanisms and Kondo effect) 73.40.Gk - Tunneling (for tunneling in quantum Hall effects, see 73.43.Jn)