Vortex lattice in two-dimensional chiral XY ferromagnets and the inverse Berezinskii-Kosterlitz-Thouless transition

TL;DR

This paper investigates vortex-antivortex lattices and inverse BKT transitions in 2D chiral XY ferromagnets with Dzyaloshinskii-Moriya interaction, revealing a novel inverse transition mechanism at high DM interaction regimes.

Contribution

It demonstrates the emergence of vortex-antivortex lattices and the occurrence of an inverse BKT transition driven by Dzyaloshinskii-Moriya interaction in 2D chiral XY ferromagnets.

Findings

Vortex-antivortex lattice appears at low temperatures with modulated DM interaction.

Standard BKT transition occurs in exchange-dominated regime.

Inverse BKT transition occurs in DM-dominated regime, with lattice melting at higher temperatures.

Abstract

In this Letter we will show that, in the presence of a properly modulated Dzyaloshinskii-Moriya (DM) interaction, a $U(1)$ vortex-antivortex lattice appears at low temperatures for a wide range of the DM interaction. Even more, in the region dominated by the exchange interaction, a standard BKT transition occurs. In the opposite regime, the one dominated by the DM interaction, a kind of inverse BKT transition (iBKT) takes place. As temperature rises, the vortex-antivortex lattice starts melting by annihilation of pairs of vortex-antivortex, in a sort of "inverse" BKT transition.