Quantum Monte Carlo simulation of two-dimensional S=1/2 antiferromagnets with very weak easy-plane anisotropy

Abstract

We study the critical and thermodynamic properties of an S=1/2 two-dimensional quantum XXZ antiferromagnet with weak easy-plane anisotropy using the continuous-time quantum Monte Carlo method based on the loop-cluster algorithm. A detailed finite-size scaling analysis reveals that the model displays a finite temperature Berezinskii–Kosterlitz–Thouless (BKT) transition for anisotropy as small as 10−3, the dominant isotropic coupling. For larger anisotropy (10−2) we single out relevant features of anisotropic behavior that anticipate the BKT transition. Implications for experimental observation of a BKT phase in real magnets are discussed.