Cuccoli Alessandro, Roscilde Tommaso, Vaia Ruggero, Verrucchi Paola
Dipartimento di Fisica, Università di Firenze, Via G. Sansone 1, I-50019 Sesto Fiorentino (FI), Italy.
Phys Rev Lett. 2003 Apr 25;90(16):167205. doi: 10.1103/PhysRevLett.90.167205. Epub 2003 Apr 24.
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 behavior. 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 noncritical 2D XY behavior. Direct comparison is made with uniform susceptibility data relative to the S=1/2 layered antiferromagnet Sr2CuO2Cl2.
我们考虑具有(S = 1/2)且易平面交换各向异性非常弱的正方晶格上的海森堡反铁磁体；借助基于连续时间回路算法的量子蒙特卡罗方法，我们发现该模型的热力学对微小各向异性的存在高度敏感，并且其特征是在各向同性和平面行为之间存在交叉。我们讨论了交叉现象背后的机制，并表明它发生在该模型特有的温度下。在交叉温度以下观察到预期的贝雷津斯基 - 科斯特利茨 - Thouless 转变：因此出现了一个有限的温度范围，可用于实验检测非临界二维 XY 行为。将其与相对于(S = 1/2)层状反铁磁体(Sr_2CuO_2Cl_2)的均匀磁化率数据进行了直接比较。
