Quantum motion and level quantization of a skyrmion in a pinning potential in chiral magnets

TL;DR

This paper investigates the quantum behavior of skyrmions in chiral magnets, revealing level quantization in pinning potentials and suggesting experimental detection via microwave absorption, especially for small skyrmions with strong Dzyaloshinskii-Moriya interactions.

Contribution

It demonstrates the quantization of skyrmion energy levels in a pinning potential and discusses observable quantum effects in small skyrmions.

Findings

Skyrmions perform cyclotron motion without pinning.

Pinning potential splits Landau levels into quantized states.

Quantum effects are enhanced in small skyrmions with strong Dzyaloshinskii-Moriya interaction.

Abstract

A new topological excitation called skyrmion has been observed experimentally in chiral magnets without spatial inversion symmetry. The dynamics of a skyrmion is equivalent to an electron moving in a strong magnetic field. As a skyrmion involves large number of spins, it is not clear whether there exist observable quantum effects. In this work, we study the quantum dynamics of a skyrmion in a pinning potential. Without a pinning potential, the skyrmion performs cyclotron motion due to the strong emergent magnetic field originating from the Berry phase of spins, and all skyrmions occupy the lowest Landau level. Their wave functions are strongly localized in a region with radius less than $1\ \AA$ when no driving force is applied. Thus in most circumstances, the quantum effects of a skyrmion are weak. In the presence of a pinning potential, the lowest Landau level for skyrmions is split into quantized levels, characterized by the orbital moments. The transition between quantized levels can be observed experimentally by microwave absorption measurements in low temperature region. The quantum effects are more prominent for a skyrmion with a small size, which can be realized in magnets with a large Dzyaloshinskii-Moriya interaction.