Ground-state phase diagram of the quantum $J_1-J_2$ model on the square lattice

TL;DR

This study maps the ground-state phase diagram of the quantum J1-J2 model on a square lattice, revealing classical magnetic orders and an intermediate topological spin liquid phase using an entangled-plaquette variational approach.

Contribution

It introduces a variational ansatz to accurately identify magnetic and spin liquid phases, including topological properties, in the J1-J2 model.

Findings

Classical Néel and collinear magnetic orders identified

Intermediate spin liquid phase found between magnetic phases

Spin liquid shown to be topological based on entanglement entropy

Abstract

We study the ground-state phase diagram of the quantum $J_1-J_2$ model on the square lattice by means of an entangled-plaquette variational ansatz. In the range $0\le {J_2}/{J_1} \le 1$, we find classical magnetic order of N\'eel and collinear type, for ${J_2}/{J_1}\lesssim 0.5$, and $J_2/J_1 \gtrsim 0.6$ respectively. For intermediate values of $J_2/J_1$ the ground state is a spin liquid (i.e., paramagnetic with no valence bond crystalline order). Our estimates of the entanglement entropy show that such a spin liquid is topological.