Phasons and excitations in skyrmion lattice

TL;DR

This paper theoretically investigates low-energy excitations in a two-dimensional skyrmion lattice, identifying phasons and a topological mode, with implications for experimental detection and stability analysis.

Contribution

It introduces a collective coordinate framework to describe skyrmion lattice excitations, revealing a new topological mode affecting stability and charge screening.

Findings

Phason spectra include a gapless quadratic mode and a massive mode.

Discovery of a collective topological mode influencing skyrmion stability.

Screening of topological charge impacts microwave absorption and Hall effects.

Abstract

Excitations of two-dimensional skyrmion lattice are theoretically studied based on a collective coordinate description. Starting from the representation of skyrmion lattice in terms of three helices, we identify the canonical coordinates describing low energy excitations as phasons. The phason excitation spectra turn out to have one gapless mode with a quadratic dispersion and one massive mode, in agreement with previous studies. We will show that there is another collective mode governing the topological nature and the stability of skyrmion lattice and that the fluctuation of this mode leads to a screening of the topological charge of the lattice. Experimental implications of the screening effect in microwave absorption, topological Hall effect and depinning threshold current in metals are discussed.