Influence of Ising-anisotropy on the zero-temperature phase transition in the square lattice spin-1/2 J-J' model

TL;DR

This study investigates how Ising-anisotropy affects the quantum phase transition in a square lattice spin-1/2 J-J' model, revealing that increased anisotropy suppresses the transition, which disappears in the Ising limit.

Contribution

It provides a detailed analysis of the influence of anisotropy on the quantum phase transition using multiple computational methods, highlighting the shift and eventual disappearance of the transition.

Findings

Transition from Néel order to quantum paramagnetic phase at J'c ~ 2.5-3J in isotropic case

Transition point J'c increases linearly with anisotropy parameter Δ

Transition disappears as Δ approaches infinity (Ising limit)

Abstract

We use a variational mean-field like approach, the coupled cluster method (CCM) and exact diagonalization to investigate the ground-state order-disorder transition for the square lattice spin-half XXZ model with two different nearest-neighbor couplings $J$ and $J'$. Increasing $J' > J$ the model shows in the isotropic Heisenberg limit a second-order transition from semi-classical N\'eel order to a quantum paramagnetic phase with enhanced local dimer correlations on the $J'$ bonds at about $J'_{c} \sim 2.5 ... 3 J$. This transition is driven by the quantum competition between $J'$ and $J$. Increasing the anisotropy parameter $\Delta> 1$ we diminish the quantum fluctuations and thus the degree of competition. As a result the transition point $J'_{c}$ is shifted to larger values. We find indications for a linear increase of $J'_{c}$ with $\Delta $, i.e. the transition disappears in the Ising limit $\Delta \to \infty$.