Dimerized phase and transitions in a spatially anisotropic square lattice antiferromagnet

TL;DR

This paper explores how quantum fluctuations in a spatially anisotropic square lattice antiferromagnet lead to a novel intermediate dimerized phase, splitting a classical transition into two quantum-critical points.

Contribution

It reveals the existence of an intermediate quantum-disordered dimer phase in an anisotropic antiferromagnet, extending understanding of quantum phase transitions in such systems.

Findings

Classical first-order transition splits into two quantum-critical points.

Discovery of an intermediate quantum-disordered columnar dimer phase.

The phase transition behavior is consistent in both 2D and ladder models.

Abstract

We investigate the spatially anisotropic square lattice quantum antiferromagnet. The model describes isotropic spin-1/2 Heisenberg chains (exchange constant J) coupled antiferromagnetically in the transverse (J_\perp) and diagonal (J_\times), with respect to the chain, directions. Classically, the model admits two ordered ground states -- with antiferromagnetic and ferromagnetic inter-chain spin correlations -- separated by a first order phase transition at J_\perp=2J_\times. We show that in the quantum model this transition splits into two, revealing an intermediate quantum-disordered columnar dimer phase, both in two dimensions and in a simpler two-leg ladder version. We describe quantum-critical points separating this spontaneously dimerized phase from classical ones.