Berry phase investigation of spin-S ladders
Berry phase investigation of spin-S ladders
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自旋-S 阶梯的贝里相研究
DOI：
10.1103/physrevb.88.184418
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发表时间：
2013
影响因子：
3.7
通讯作者：
F. Mila
中科院分区：
文献类型：
--
作者：
Natalia Chepiga;F. Michaud;F. Mila
我们研究了反铁磁自旋S阶梯的性质与当地的Berry相定义的一个或几个本地债券的扭曲的帮助下。在具有时间反演对称性的带隙系统中，这些贝里相位是量子化的，因此原则上能够表征不同的相位。在一个完全受挫的阶梯上的总自旋是一个保守的量，突然增加的梯级耦合的情况下，我们表明，两个贝里阶段是相关的检测这样的相变：通过施加扭曲的一个梯级耦合定义的梯级贝里阶段，和扭曲贝里阶段定义的边界条件沿着腿。在的情况下，nonfrustrated梯子，我们遵循的命运贝里阶段之间的标准梯子和二聚自旋链插值时，令人惊讶的结论是，至少足够远的二聚链，他们定义不同的域在参数空间。对自旋能隙和边缘态的仔细研究表明，扭转贝里相位的变化与体能隙关闭的量子相变有关，并且在适当的边界条件下，边缘态出现或消失，而横档贝里相位的变化不一定与量子相变有关。对于规则阶梯，差异特别尖锐，其中当梯级耦合从零增加到无穷大时，扭曲Berry相位根本不改变，而梯级Berry相位改变2S次。通过与完全受挫的梯子类比，这些变化被解释为区域之间的交叉，其中梯级处于从强梯级极限中的0到弱梯级极限中的2S的总自旋的不同状态。这种解释得到了以下观察结果的进一步支持：如果一个横档是强铁磁的，或者等效地，如果一个横档被自旋2S杂质取代，则这些交叉会根据横档耦合而变成真实的相变。
We investigate the properties of antiferromagnetic spin-S ladders with the help of local Berry phases defined by imposing a twist on one or a few local bonds. In gapped systems with time-reversal symmetry, these Berry phases are quantized, hence able in principle to characterize different phases. In the case of a fully frustrated ladder where the total spin on a rung is a conserved quantity that changes abruptly upon increasing the rung coupling, we show that two Berry phases are relevant to detect such phase transitions: the rung Berry phase defined by imposing a twist on one rung coupling, and the twist Berry phase defined by twisting the boundary conditions along the legs. In the case of nonfrustrated ladders, we have followed the fate of both Berry phases when interpolating between standard ladders and dimerized spin chains, with the surprising conclusion that, at least far enough from dimerized chains, they define different domains in parameter space. A careful investigation of the spin gap and of edge states shows that a change of twist Berry phase is associated with a quantum phase transition at which the bulk gap closes, and at which, with appropriate boundary conditions, edge states appear or disappear, while a change of rung Berry phase is not necessarily associated with a quantum phase transition. The difference is particularly acute for regular ladders, in which the twist Berry phase does not change at all upon increasing the rung coupling from zero to infinity while the rung Berry phase changes 2S times. By analogy with the fully frustrated ladder, these changes are interpreted as crossovers between domains in which the rungs are in different states of total spin from 0 in the strong rung limit to 2S in the weak rung limit. This interpretation is further supported by the observation that these crossovers turn into real phase transitions as a function of rung coupling if one rung is strongly ferromagnetic, or equivalently if one rung is replaced by a spin 2S impurity.