Layered ferromagnet-superconductor structures: The π state and proximity effects

Abstract

We investigate clean mutilayered structures of the SFS and SFSFS type (where the S layer is intrinsically superconducting and the F layer is ferromagnetic), at low temperature, through numerical solution of the self-consistent Bogoliubov–de Gennes equations for these systems. We obtain results for the pair amplitude, the local density of states, and the local magnetic moment. We find that as a function of the thickness dF of the magnetic layers separating adjacent superconductors, the ground state energy varies periodically between two stable states. The first state is an ordinary “0 state,” in which the order parameter has a phase difference of zero between consecutive S layers, and the second is a “π state,” where the sign alternates, corresponding to a phase difference of π between adjacent S layers. This behavior can be understood from simple arguments. The density of states and the local magnetic moment also reflect this periodicity.

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