Interference phenomena and long-range proximity effect in clean superconductor-ferromagnet systems.

We study peculiarities of the proximity effect in clean superconductor-ferromagnet structures caused by either the spatial or momentum dependence of the exchange field. Even a small modulation of the exchange field along the quasiparticle trajectories is shown to provide a long-range contribution to the supercurrent due to the specific interference of particle- and holelike wave functions. The momentum dependence of the exchange field caused by the spin-orbit interaction results in long-range superconducting correlations even in the absence of a ferromagnetic domain structure and can explain recent experiments on ferromagnetic nanowires.