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Detection of XY behaviour in weakly anisotropic quantum antiferromagnets on the square lattice

Alessandro Cuccoli·Tommaso Roscilde·Ruggero Vaia·Paola Verrucchi
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Abstract

We consider the Heisenberg antiferromagnet on the square lattice with S=1/2 and very weak easy-plane exchange anisotropy; by means of the quantum Monte Carlo method, based on the continuous-time loop algorithm, we find that the thermodynamics of the model is highly sensitive to the presence of tiny anisotropies and is characterized by a crossover between isotropic and planar behaviour. We discuss the mechanism underlying the crossover phenomenon and show that it occurs at a temperature which is characteristic of the model. The expected Berezinskii-Kosterlitz-Thouless transition is observed below the crossover: a finite range of temperatures consequently opens for experimental detection of non-critical 2D XY behaviour. Direct comparison is made with uniform susceptibility data relative to the S=1/2 layered antiferromagnet Sr2CuO2Cl2.

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Alessandro Cuccoli, Tommaso Roscilde, Ruggero Vaia, Paola Verrucchi. 2003-04-18. Detection of XY behaviour in weakly anisotropic quantum antiferromagnets on the square lattice. https://doi.org/10.1103/physrevlett.90.167205

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