First order transition between magnetic order and valence-bond order in a 2D frustrated Heisenberg model

TL;DR

This paper investigates the phase transition between magnetic and valence bond order in a 2D frustrated Heisenberg model, revealing a first-order transition within the magnetically ordered phase using multiple theoretical approaches.

Contribution

It demonstrates that the transition between magnetic and valence bond order in the model is first-order, using exact diagonalisation, spin wave theory, and Schwinger boson mean field theory.

Findings

Transition is first-order

Transition occurs within magnetically ordered phase

Multiple theoretical methods confirm results

Abstract

We study the competition between magnetic order and valence bond order in a two dimensional (2D) frustrated Heisenberg model introduced some time ago by Shastry and Sutherland ({\sc B. Sriram Shastry} and {\sc Bill Sutherland}, {\em Physica} 108{\bf B},1069 (1981) ) for which a configuration of dimers is known to be the ground state in a certain range of parameters. Using exact diagonalisation of small clusters, linear spin wave theory and Schwinger boson mean field theory, we show that the transition between the two types of order is first-order, and that it takes place inside the domain where magnetic long-range order is stable with respect to quantum fluctuations.