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

R. Darradi·J. Richter·S. E. Krueger
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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 Néel 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 $Δ> 1$ 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 $Δ$, i.e. the transition disappears in the Ising limit $Δ\to \infty$.

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R. Darradi, J. Richter, S. E. Krueger. 2004-10-27. Influence of Ising-anisotropy on the zero-temperature phase transition in the square lattice spin-1/2 J-J' model. https://doi.org/10.1088/0953-8984%2F16%2F15%2F019

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