Polyhexatic and Polycrystalline States of Skyrmion Lattices

TL;DR

This study uses Monte Carlo simulations to explore the phase transitions of skyrmion lattices, revealing the formation of polycrystalline and polyhexatic states through temperature variations.

Contribution

It provides the first detailed Monte Carlo analysis of skyrmion lattice phase transitions, including the discovery of polyhexatic states.

Findings

Cooling from high temperature forms a skyrmion polycrystal.

Heating a perfect skyrmion lattice causes a first-order melting into a polyhexatic state.

Further heating leads to a disordered skyrmion liquid.

Abstract

Abstract We report Monte Carlo studies of lattices of up to $10^{5}$ skyrmions treated as particles with negative core energy and repulsive interaction obtained from a microscopic spin model. Temperature dependence of translational and orientational correlations has been investigated for different experimental protocols and initial conditions. Cooling the skyrmion liquid from fully disordered high-temperature state results in the formation of a skyrmion polycrystal. A perfect skyrmion lattice prepared at $T=0$, on raising temperature undergoes a first-order melting transition into a polyhexatic state that consists of large orientationally ordered domains of fluctuating shape. On the further increasing temperature, these domains decrease in size, leading to a fully disordered liquid of skyrmions.