Department of Physics, University of Wisconsin, 1150 University Avenue, Madison, Wisconsin 53706, USA.
Phys Rev Lett. 2012 Nov 2;109(18):187201. doi: 10.1103/PhysRevLett.109.187201.
We study the critical properties of the Kitaev-Heisenberg model on the honeycomb lattice at finite temperatures that might describe the physics of the quasi-two-dimensional compounds, Na(2)IrO(3) and Li(2)IrO(3). The model undergoes two phase transitions as a function of temperature. At low temperature, thermal fluctuations induce magnetic long-range order by the order-by-disorder mechanism. This magnetically ordered state with a spontaneously broken Z(6) symmetry persists up to a certain critical temperature. We find that there is an intermediate phase between the low-temperature, ordered phase and the high-temperature, disordered phase. Finite-sized scaling analysis suggests that the intermediate phase is a critical Kosterlitz-Thouless phase with continuously variable exponents. We argue that the intermediate phase has been observed above the low-temperature, magnetically ordered phase in Na(2)IrO(3), and also, likely exists in Li(2)IrO(3).
我们研究了有限温度下的海森堡- Kitaev 模型在蜂窝晶格上的临界性质，这些性质可能描述了准二维化合物 Na(2)IrO(3)和 Li(2)IrO(3)的物理性质。该模型随着温度的变化经历了两次相变。在低温下，热涨落通过无序机制诱导磁长程有序。这种具有自发破缺 Z(6)对称性的磁有序状态一直持续到一定的临界温度。我们发现，在低温有序相和高温无序相之间存在一个中间相。有限大小的标度分析表明，中间相是一个具有连续变化指数的临界 Kosterlitz-Thouless 相。我们认为，在 Na(2)IrO(3)中，中间相已经在低温磁有序相之上被观察到，并且在 Li(2)IrO(3)中也可能存在。
