New ordered phases in a class of generalized XY models

TL;DR

This paper investigates generalized XY models with higher order harmonics, revealing new ordered phases and phase transitions belonging to various universality classes through extensive Monte Carlo simulations.

Contribution

It introduces a comprehensive analysis of higher order harmonic effects in XY models, uncovering novel ordered phases and phase transition behaviors.

Findings

Discovery of additional ordered phases due to higher harmonics

Identification of phase transitions in Potts, Ising, and KT universality classes

Complex phase diagram with competing ferromagnetic and pseudonematic couplings

Abstract

It is well known that the 2D XY model exhibits an unusual infinite order phase transition belonging to the Kosterlitz-Thouless (KT) universality class. Introduction of a nematic coupling into the XY Hamiltonian leads to an additional phase transition in the Ising universality class [D.H. Lee and G. Grinstein, Phys. Rev. Lett. 55, 541 (1985)]. Using a combination of extensive Monte Carlo simulations and finite size scaling, we show that the higher order harmonics lead to a qualitatively different phase diagram, with additional ordered phases originating from the competition between the ferromagnetic and pseudonematic couplings. The new phase transitions belong to the 2D Potts, Ising, or KT universality classes.