Spin-precession-assisted supercurrent in a superconducting quantum point contact coupled to a single-molecule magnet

TL;DR

This paper investigates how the precession of a nanomagnet's spin influences supercurrent in a superconducting quantum point contact, revealing non-equilibrium effects and potential for temperature-based control.

Contribution

It introduces a microscopic model showing how spin precession affects supercurrent and quasiparticle populations, highlighting new control mechanisms in superconducting spintronics.

Findings

Precession induces transitions affecting charge and spin currents.

Supercurrent is enhanced and modified by spin dynamics.

Temperature can tune the back-action on the precessing spin.

Abstract

The supercurrent of a quantum point contact coupled to a nanomagnet strongly depends on the dynamics of the nanomagnet's spin. We employ a fully microscopic model to calculate the transport properties of a junction coupled to a spin whose dynamics is modeled as Larmor precession brought about by an external magnetic field and find that the dynamics affects the charge and spin currents by inducing transitions between the continuum states below the superconducting gap edge and the Andreev levels. This redistribution of the quasiparticles leads to a non-equilibrium population of the Andreev levels and an enhancement of the supercurrent which is visible as a modified current-phase relation as well as a non-monotonous critical current as function of temperature. The non-monotonous behavior is accompanied by a corresponding change in spin-transfer torques acting on the precessing spin and leads to the possibility of using temperature as a means to tune the back-action on the spin.