Energy gap of ferromagnet-superconductor bilayers

TL;DR

This paper calculates the energy gap in ferromagnet-superconductor bilayers using self-consistent theory, revealing how the gap depends on ferromagnetic layer thickness, interface quality, and Fermi energy mismatch, with implications for quasiparticle excitations.

Contribution

It provides a detailed theoretical analysis of the energy gap behavior in ferromagnet-superconductor bilayers considering various physical parameters.

Findings

The energy gap diminishes as ferromagnetic layer thickness increases.

Interface quality and Fermi energy mismatch significantly influence the energy gap.

Density of states results are consistent with the calculated energy gap.

Abstract

The excitation spectrum of clean ferromagnet-superconductor bilayers is calculated within the framework of the self-consistent Bogoliubov-de Gennes theory. Because of the proximity effect, the superconductor induces a gap in the ferromagnet spectrum, for thin ferromagnetic layers. The effect depends strongly on the exchange field in the ferromagnet. We find that as the thickness of the ferromagnetic layer increases, the gap disappears, and that its destruction arises from those quasiparticle excitations with wavevectors mainly along the interface. We discuss the influence that the interface quality and Fermi energy mismatch between the ferromagnet and superconductor have on the calculated energy gap. We also evaluate the density of states in the ferromagnet, and we find it in all cases consistent with the gap results.