Quantum Depinning of a Magnetic Skyrmion

TL;DR

This paper explores the quantum tunneling behavior of magnetic skyrmions in insulators, providing universal formulas for tunneling rates and crossover temperatures, and demonstrating that small skyrmions can exhibit quantum properties at millikelvin temperatures.

Contribution

It introduces a universal approach to analyze quantum depinning of skyrmions, independent of specific pinning potentials, and applies it to realistic materials like Cu2OSeO3.

Findings

Universal WKB exponent for tunneling rate

Crossover temperature between thermal and quantum regimes

Small skyrmions (~10 lattice sites) can act as quantum objects at mK temperatures

Abstract

We investigate the quantum depinning of a weakly driven skyrmion out of an impurity potential in a mesoscopic magnetic insulator. For small barrier height, the Magnus force dynamics dominates over the inertial one, and the problem is reduced to a massless charged particle in a strong magnetic field. The universal form of the WKB exponent, the rate of tunneling, and the crossover temperature between thermal and quantum tunneling is provided, independently of the detailed form of the pinning potential. The results are discussed in terms of macroscopic parameters of the insulator Cu2OSeO3 and various skyrmion radii. We demonstrate that small enough magnetic skyrmions, with a radius of ~ 10 lattice sites, consisting of some thousands of spins, can behave as quantum objects at low temperatures in the mK regime.