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arXiv 1012.4491cond-mat.str-elcond-mat.quant-gascond-mat.stat-mech
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有序矢量优化的修正自旋波理论II:空间各向异性三角晶格和含海森堡相互作用的$J_1J_2J_3$模型

Modified spin-wave theory with ordering vector optimization II: Spatially anisotropic triangular lattice and $J_1J_2J_3$ model with Heisenberg interactions

Philipp Hauke, Tommaso Roscilde, Valentin Murg, J. Ignacio Cirac, Roman Schmied

摘要:

利用Takahashi的改进的自旋波(MSW)理论和序矢量优化方法,研究了空间各向异性三角晶格和次近邻耦合正方晶格($J_1J_2J_3$模型)上$S=1/2$海森堡量子反铁磁体的基态相位.我们比较了MSW的结果与精确对角化和投影纠缠对态的计算,证明其定性和定量的可靠性。我们发现,MSW理论正确地占强大的量子效应的磁相位的有序矢量的模型正在调查中:特别是共线磁秩序促进非共线(螺旋)秩序的费用,和几个螺旋状态,这是稳定的经典水平,从量子相图消失。此外,共线态和非共线态从来没有连续连接,但它们被MSW分解的参数区域分开,表明可能出现非磁性基态。在空间各向异性的三角形晶格的情况下,一个大的击穿区域也出现在弱耦合链之间构成的晶格,这表明可能发生的一个大的非磁性区域连续连接的自旋液体状态的非耦合链。

英文摘要:

We study the ground state phases of the $S=1/2$ Heisenberg quantum antiferromagnet on the spatially anisotropic triangular lattice and on the square lattice with up to next-next-nearest neighbor coupling (the $J_1J_2J_3$ model), making use of Takahashi's modified spin-wave (MSW) theory supplemented by ordering vector optimization. We compare the MSW results with exact diagonalization and projected-entangled-pair-states calculations, demonstrating their qualitative and quantitative reliability. We find that MSW theory correctly accounts for strong quantum effects on the ordering vector of the magnetic phases of the models under investigation: in particular collinear magnetic order is promoted at the expenses of non-collinear (spiral) order, and several spiral states which are stable at the classical level, disappear from the quantum phase diagram. Moreover, collinear states and non-collinear ones are never connected continuously, but they are separated by parameter regions in which MSW breaks down, signaling the possible appearance of a non-magnetic ground state. In the case of the spatially anisotropic triangular lattice, a large breakdown region appears also for weak couplings between the chains composing the lattice, suggesting the possible occurrence of a large non-magnetic region continuously connected with the spin-liquid state of the uncoupled chains.

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