Gapped spin liquid phase in the J1-J2 Heisenberg model by a Bosonic resonating valence-bond ansatz

TL;DR

This paper investigates the phase diagram of the J1-J2 Heisenberg model on a square lattice using a Bosonic RVB wave function, revealing a stable gapped Z2 spin liquid phase with specific transition points.

Contribution

It introduces a Bosonic RVB ansatz combined with variational Monte Carlo to accurately describe a gapped spin liquid in the J1-J2 model, contrasting with previous Fermionic approaches.

Findings

Discovery of a stable Z2 spin liquid phase between antiferromagnetic phases.

Identification of a continuous transition at J2=0.4J1.

Observation of a non-monotonic triplet gap behavior.

Abstract

We study the ground-state phase diagram of the spin-1/2 J1-J2 Heisenberg model on the square lattice with an accurate Bosonic resonating valence-bond (RVB) wave function. In contrast to the RVB ansatz based on Schwinger Fermions, the representation based on Schwinger Bosons, supplemented by a variational Monte Carlo technique enforcing the exact projection onto the physical subspace, is able to describe a fully gapped spin liquid in the strongly frustrated regime. In particular, a fully symmetric Z2 spin liquid is stable between two antiferromagnetic phases; a continuous transition at J2=0.4J1, when the Marshall sign rule begins to be essentially violated, and a first-order transition around J2=0.6J1 are present. Most importantly, the triplet gap is found to have a non-monotonic behavior, reaching a maximum around J2=0.51J1, when the lowest spinon excitation moves from the \Gamma to the M point, i.e., k=(\pi,0).