Nonlinear Sigma model method for the J1-J2 Heisenberg model: disordered ground state with plaquette symmetry

TL;DR

This paper introduces a new nonlinear sigma model approach for the 2D J1-J2 Heisenberg model, revealing a continuous disordered phase with plaquette symmetry that extends across different regimes.

Contribution

A novel nonlinear sigma model method is developed that accurately captures the disordered ground state with plaquette symmetry in the J1-J2 model.

Findings

Disordered phase extends from frustrated to unfrustrated regimes.

Ground states are plaquette states with four-fold degeneracy.

Method preserves original spin degrees of freedom.

Abstract

A novel nonlinear sigma model method is proposed for the two-dimensional J1-J2 model, which is extended to include plaquette-type distortion. The nonlinear sigma model is properly derived without spoiling the original spin degrees of freedom. The method shows that a single disordered phase continuously extends from a frustrated uniform regime to an unfrustrated distorted regime. By the continuity and Oshikawa's commensurability condition, the disordered ground states for the uniform J1-J2 model are plaquette states with four-fold degeneracy.