First-order phase transition in easy-plane quantum antiferromagnets

TL;DR

This paper investigates the nature of quantum phase transitions in easy-plane quantum antiferromagnets, using large-scale Monte Carlo simulations, and finds evidence for a first-order transition contrary to previous conjectures of a second-order transition.

Contribution

It provides the first large-scale numerical evidence that the phase transition in the studied system is first-order, challenging the deconfined quantum criticality scenario.

Findings

The transition is first-order, not second-order.

Monte Carlo simulations include a Berry phase term.

Contradicts previous conjectures about the transition nature.

Abstract

Quantum phase transitions in Mott insulators do not fit easily into the Landau-Ginzburg-Wilson paradigm. A recently proposed alternative to it is the so called deconfined quantum criticality scenario, providing a new paradigm for quantum phase transitions. In this context it has recently been proposed that a second-order phase transition would occur in a two-dimensional spin 1/2 quantum antiferromagnet in the deep easy-plane limit. A check of this conjecture is important for understanding the phase structure of Mott insulators. To this end we have performed large-scale Monte Carlo simulations on an effective gauge theory for this system, including a Berry phase term that projects out the $S=1/2$ sector. The result is a first-order phase transition, thus contradicting the conjecture.