Spin-polarized quasiparticle control in a double spin-filter tunnel junction

TL;DR

This study demonstrates control over spin-polarized quasiparticles in a double spin-filter tunnel junction, revealing how nonequilibrium quasiparticle accumulation affects tunneling spectra and magnetic states.

Contribution

It introduces a novel NbN-GdN-Ti-GdN-NbN junction with magnetic decoupling and analyzes spin-polarized quasiparticle behavior through conductance and hysteresis measurements.

Findings

Hysteretic R-H loop with higher resistance in antiparallel state

Disappearance of hysteresis at sub-gap bias current

Suppression of interlayer coupling due to quasiparticle accumulation

Abstract

Spin-polarized quasiparticles can be easily created during spin-filtering through a ferromagnetic insulator (FI) in contact with a superconductor due to pair breaking effects at the interface. A combination FI-N-FI sandwiched between two superconductors can be used to create and analyze such spin-polarized quasiparticles through their nonequilibrium accumulation in the middle metallic (N) layer. We report spin-polarized quasiparticle regulation in a double spin-filter tunnel junction in the configuration NbN-GdN1-Ti-GdN2-NbN. The middle Ti layer provides magnetic decoupling between two ferromagnetic GdN and a place for nonequilibrium quasiparticle accumulation. The two GdN(1,2) layers were deposited under different conditions to introduce coercive contrast. The quasiparticle tunneling spectra has been measured at different temperatures to understand the tunneling mechanism in these double spin-filter junctions. The conductance spectra were found to be comparable to an asymmetric SINI'S-type tunnel junction. A hysteretic R-H loop with higher resistance for the antiparallel configuration compared to parallel state was observed asserting the spin-polarized nature of quasiparticles. The hysteresis in the R-H loop was found to disappear for sub-gap bias current. This difference can be understood by considering suppression of the interlayer coupling due to nonequilibrium spin-polarized quasiparticle accumulation in the Ti layer.