Superconducting cross-correlations in ferromagnets: implications for thermodynamics and quantum transport

It is demonstrated that non-local Cooper pairs can propagate in ferromagnet ic electrodes with opposite spin orientations. In the presence of such cros scorrelations, the superconducting gap is found to depend explicitly on the relative orientation of the ferromagnetic electrodes. Non-local Cooper pai rs can in principle be probed by means of direct-current (dc) transport. Fo r two ferromagnetic electrodes, we propose a 'quantum switch' that can be u sed to detect correlated pairs of electrons. For three or more ferromagneti c electrodes, the Cooper pair-like state is a linear superposition of Coope r pairs which could be detected in the dc transport. The effect also induce s an enhancement of the ferromagnetic proximity effect on the basis of supe rconducting crosscorrelations propagating along domain walls.