Signatures of a liquid-crystal transition in spin-wave excitations of skyrmions

TL;DR

This paper investigates the spin-wave excitations in skyrmion crystals, revealing distinct modes and a liquid-like precursor phase near the transition, with implications for experimental detection in magnetic materials.

Contribution

It provides the first detailed computation of the spin-wave spectrum in skyrmion crystals near the phase transition, highlighting a liquid-like precursor regime.

Findings

Six spin-wave modes within the SkX

Identification of a diffusive precursor regime above the transition temperature

Potential for detecting skyrmion spin waves via inelastic neutron scattering

Abstract

Understanding the spin-wave excitations of chiral magnetic order, such as the skyrmion crystal (SkX), is of fundamental interest to confirm such exotic magnetic order. The SkX is realized by competing Dzyaloshinskii-Moriya and ferromagnetic-exchange interactions with a magnetic field or anisotropy. Here we compute the dynamical spin structure factor, using Monte Carlo and spin dynamics simulations, extracting the spin-wave spectrum in the SkX, in the vicinity of the paramagnet to SkX transition. Inside the SkX, we find six spin-wave modes, which are supplemented by another mode originating from the ferromagnetic background. Above the critical temperature $T_s$ for the skyrmion crystallization, we find a diffusive regime, reminiscent of the liquid-to-crystal transition, revealing that topological spin texture of skyrmionic character starts to develop above $T_s$ as the precursor of the SkX. We discuss the opportunities for the detection of the spin waves of the SkX using inelastic-neutron-scattering experiments in manganite-iridate heterostructures.