论文标题

蜂窝状晶格上改良整数旋转基塔夫模型的热力学行为

Thermodynamic behavior of modified integer-spin Kitaev models on the honeycomb lattice

论文作者

Bradley, Owen, Oitmaa, Jaan, Sen, Diptiman, Singh, Rajiv R. P.

论文摘要

我们研究了Baskaran,Sen和Shankar引入的改性自旋型$ KITAEV模型的热力学特性(Phys。B78,115116(2008))。这些模型的特性对于半odd-Integer旋转其本征态映射到Spin-1/2 Kitaev模型的特征,并具有众所周知的高度纠缠的量子自旋式液体状态和Majorana fermions。对于整数旋转,哈密顿量是由通勤的当地运营商制成的。因此,可以选择本征态在不同位点之间完全未进入,尽管每个本征态具有显着的变性。对于一半的启动,热力学特性可能与Spin-1/2 Kitaev模型有关,除了额外的退化。因此,我们将重点放在整数旋转的情况下。我们使用转移矩阵方法,高温膨胀和蒙特卡洛模拟来研究具有旋转$ s = 1 $和$ s = 2 $的铁磁和反铁磁模型的热力学特性。除了所有模型都具有的大型残留熵外,我们发现它们可以具有多种不同的行为。传输矩阵计算表明,对于不同的模型,相关长度可以是有限的,为$ t \至0 $,至关重要的是$ t \ to $ t \ to 0 $或以$ t \ to -t \至0 $的指数分发。每个型号$+1 $ as act AS $ t \ rightArrow0 $在所有型号中都有一个保守的$ z_2 $通量变量,除$ s = 1 $ antiferRomagnet外,平均磁带均保持为零,但在所有型号中,$ t \ rightarrow0 $均为$ t \ to $ t \ to 0 $。我们为这些结果提供定性解释。

We study the thermodynamic properties of modified spin-$S$ Kitaev models introduced by Baskaran, Sen and Shankar (Phys. Rev. B 78, 115116 (2008)). These models have the property that for half-odd-integer spins their eigenstates map on to those of spin-1/2 Kitaev models, with well-known highly entangled quantum spin-liquid states and Majorana fermions. For integer spins, the Hamiltonian is made out of commuting local operators. Thus, the eigenstates can be chosen to be completely unentangled between different sites, though with a significant degeneracy for each eigenstate. For half-odd-integer spins, the thermodynamic properties can be related to the spin-1/2 Kitaev models apart from an additional degeneracy. Hence we focus here on the case of integer spins. We use transfer matrix methods, high temperature expansions and Monte Carlo simulations to study the thermodynamic properties of ferromagnetic and antiferromagnetic models with spin $S=1$ and $S=2$. Apart from large residual entropies, which all the models have, we find that they can have a variety of different behaviors. Transfer matrix calculations show that for the different models, the correlation lengths can be finite as $T\to 0$, become critical as $T\to 0$ or diverge exponentially as $T\to 0$. There is a conserved $Z_2$ flux variable associated with each hexagonal plaquette which saturates at the value $+1$ as $T\rightarrow0$ in all models except the $S=1$ antiferromagnet where the mean flux remains zero as $T\to 0$. We provide qualitative explanations for these results.

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