Inhomogeneous Superconductivity Induced in a Ferromagnet by Proximity Effect

Abstract

Planar tunneling spectroscopy reveals damped oscillations of the superconducting order parameter induced into a ferromagnetic thin film by the proximity effect. The oscillations are due to the finite momentum transfer provided for Cooper pairs by the splitting of the spin-up and spin-down bands in the ferromagnet. As a consequence, for negative values of the superconducting order parameter the tunneling spectra are capsized (“ $\pi$ state”). The oscillations' damping and period are set by the same length scale, which depends on the spin polarization.