Breaking of Coulomb blockade by macrospin-assisted tunneling

TL;DR

This paper explores how macrospin-assisted tunneling can weaken or eliminate Coulomb blockade in a single tunnel junction, revealing a new way to control spin currents and measure magnetization dynamics in mesoscopic systems.

Contribution

It demonstrates that macrospin dynamics can influence Coulomb blockade, providing a novel method to control and measure spin-dependent tunneling in mesoscopic spintronic devices.

Findings

Macrospin-assisted tunneling can break Coulomb blockade.

Magnetization dynamics affect tunneling behavior.

Current-voltage characteristics reveal macrospin states.

Abstract

A magnet with precessing magnetization pumps a spin current into adjacent leads. As a special case of this spin pumping, a precessing macrospin (magnetization) can assist electrons in tunneling. In small systems, however, the Coulomb blockade effect can block the transport of electrons. Here, we investigate the competition between macrospin-assisted tunneling and Coulomb blockade for the simplest system where both effects meet; namely, for a single tunnel junction between a normal metal and a metallic ferromagnet with precessing magnetization. By combining Fermi's golden rule with magnetization dynamics and charging effects, we show that the macrospin-assisted tunneling can soften or even break the Coulomb blockade. The details of these effects -- softening and breaking of Coulomb blockade -- depend on the macrospin dynamics. This allows, for example, to measure the macrospin dynamics via a system's current-voltage characteristics. It also allows to control a spin current electrically. From a general perspective, our results provide a platform for the interplay between spintronics and electronics on the mesoscopic scale. We expect our work to provide a basis for the study of Coulomb blockade in more complicated spintronic systems.