Condensed Matter Theory Laboratory, RIKEN, Saitama 351-0198, Japan.
Condensed Matter Theory Laboratory, RIKEN, Saitama 351-0198, Japan and Research and Education Center for Natural Sciences, Keio University, Kanagawa 223-8521, Japan.
Phys Rev Lett. 2014 Mar 28;112(12):127203. doi: 10.1103/PhysRevLett.112.127203. Epub 2014 Mar 26.
The triangular lattice of S=1/2 spins with XXZ anisotropy is a ubiquitous model for various frustrated systems in different contexts. We determine the quantum phase diagram of the model in the plane of the anisotropy parameter and the magnetic field by means of a large-size cluster mean-field method with a scaling scheme. We find that quantum fluctuations break up the nontrivial continuous degeneracy into two first-order phase transitions. In between the two transition boundaries, the degeneracy-lifting results in the emergence of a new coplanar phase not predicted in the classical counterpart of the model. We suggest that the quantum phase transition to the nonclassical coplanar state can be observed in triangular-lattice antiferromagnets with large easy-plane anisotropy or in the corresponding optical-lattice systems.
具有 XXZ 各向异性的 S=1/2 自旋三角晶格是不同背景下各种受挫系统的通用模型。我们通过具有缩放方案的大尺寸团簇平均场方法来确定模型在各向异性参数和磁场平面中的量子相图。我们发现，量子涨落打破了非平凡的连续简并，导致两个一级相变。在两个相变边界之间，简并消除导致了模型经典对应物中没有预测到的新共面相的出现。我们提出，在具有大易面各向异性的三角晶格反铁磁体或相应的光晶格系统中，可以观察到量子相变为非经典共面态的转变。
