Spontaneous Spin Polarized Currents in Superconductor-Ferromagnetic Metal Heterostructures

TL;DR

This paper investigates how certain ferromagnetic-superconductor heterostructures can spontaneously generate spin-polarized currents due to Andreev bound states near zero energy, with the polarization depending on band filling.

Contribution

It introduces a microscopic model showing spontaneous spin-polarized currents in ferromagnetic-superconductor heterostructures and analyzes their dependence on band filling.

Findings

Spontaneous spin-polarized currents occur at specific exchange splitting values.

Andreev bound states near zero energy support these currents.

Spin polarization of currents depends on band filling.

Abstract

We study a simple microscopic model for thin, ferromagnetic, metallic layers on semi-infinite bulk superconductor. We find that for certain values of the exchange spliting, on the ferromagnetic side, the ground states of such structures feature spontaneously induced spin polarized currents. Using a mean-field theory, which is selfconsistent with respect to the pairing amplitude $\chi$, spin polarization $\vec{m}$ and the spontaneous current $\vec{j}_s$, we show that not only there are Andreev bound states in the ferromagnet but when their energies $E_n$ are near zero they support spontaneous currents parallel to the ferromagnetic-superconducting interface. Moreover, we demonstrate that the spin-polarization of these currents depends sensitively on the band filling.