Boson pairing and unusual criticality in a generalized XY model

TL;DR

This paper investigates a generalized XY model with mixed couplings, revealing unique critical behavior and phase transitions involving vortices, half-vortices, and condensate phases, using theoretical and simulation methods.

Contribution

It introduces a generalized XY model with mixed periodic couplings and demonstrates novel critical phenomena and phase transitions through field theory and Monte Carlo simulations.

Findings

Direct transition from disordered to single-particle condensate via Ising transition

Presence of vortices and half-vortices enables multiple condensate phases

Unusual criticality similar to deconfined criticality scenario

Abstract

We discuss the unusual critical behavior of a generalized XY model containing both 2\pi-periodic and \pi-periodic couplings between sites. The presence of vortices and half-vortices allows for single-particle condensate and pair-condensate phases. Using a field theoretic formulation and worm algorithm Monte Carlo simulations, we show that in two dimensions it is possible for the system to pass directly from the disordered (high temperature) phase to the single particle (quasi)-condensate via an Ising transition, a situation reminiscent of the `deconfined criticality' scenario.