Charge and spin transport through a ferromagnet/insulator/unconventional superconductor junction

TL;DR

This paper investigates charge and spin transport in a ferromagnet/insulator/unconventional superconductor junction, revealing how different ferromagnetic mechanisms and superconductor symmetries influence conductance and spin current, with potential for spintronic applications.

Contribution

It introduces a model analyzing how ferromagnetism driven by spin bandwidth asymmetry or Stoner splitting affects charge and spin transport in unconventional superconductor junctions.

Findings

Charge conductance features reveal ferromagnetism mechanisms and order parameter symmetry.

Time-reversal symmetry breaking superconductors can be distinguished using ferromagnetic probes.

Spin bandwidth asymmetry ferromagnets can support larger spin currents than Stoner ferromagnets.

Abstract

We analyze the charge and spin transport through a ballistic ferromagnet/insulator/superconductor junction by means of the Bogoliubov-de Gennes equations. For the ferromagnetic side we assume that ferromagnetism may be driven by an unequal mass renormalization of oppositely polarized carriers, i.e. a spin bandwidth asymmetry, and/or by a rigid splitting of up-and down-spin electron bands, as in a standard Stoner ferromagnet, whereas the superconducting side is assumed to exhibit a d-wave symmetry of the order parameter, which can be pure or accompanied by a minority component breaking time-reversal symmetry. Several remarkable features in the charge conductance arise in this kind of junction, providing useful information about the mechanism of ferromagnetism in the ferromagnetic electrode, as well as of the order parameter symmetry in the superconducting one. In particular, we show that when a time-reversal symmetry breaking superconductor is considered, the use of the two kinds of ferromagnet mentioned above represents a valuable tool to discriminate between the different superconducting mixed states. We also explain how this junction may mimic a switch able to turn on and off a spin current, leaving the charge conductance unchanged, and we show that for a wide range of insulating barrier strengths, a spin bandwidth asymmetry ferromagnet may support a spin current larger than a standard Stoner one.