arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1206.6803cond-mat.str-el
收藏

相关价键态

Correlated valence-bond states

Yu-Cheng Lin, Ying Tang, Jie Lou, Anders W. Sandvik

摘要:

研究了S=1/2量子自旋系统价键基单重扇形振幅积(AP)态的推广。在标准AP态中,系统平铺成价键(两个自旋的单线态)的权重是取决于键长的振幅的乘积。我们在这里介绍相关AP(CAP)状态,其中振幅积进一步乘以取决于连接到一对站点(这里是最近的邻居)的两个键的因子。虽然标准的AP状态可以描述一个反铁磁(Neel)状态和价键固体(VBS)之间的相变在一维(我们也在这里研究),在二维它不能描述VBS顺序。在CAP态下,Neel-VBS跃迁被实现为描述键相关性的一些参数的函数。本文研究了正方晶格上CAP波函数的这种相变。我们发现直接的一阶Neel-VBS跃迁的例子,以及在Neel和VBS状态之间存在扩展的U(1)自旋液相的情况。在后一种情况下,过渡是连续的,我们提取临界指数和解决的问题,可能出现的U(1)对称性在近临界VBS。我们还考虑变分优化CAP状态的标准海森堡模型在一个和两个维度和J-Q模型在两个维度,后者包括四个自旋相互作用(Q)除了海森堡交换(J)和窝藏VBS秩序大Q/J。优化CAP状态导致显着降低变分能量比简单的AP状态,这些模型。

英文摘要:

We study generalizations of the singlet-sector amplitude-product (AP) states in the valence-bond basis of S=1/2 quantum spin systems. In the standard AP states, the weight of a tiling of the system into valence bonds (singlets of two spins) is a product of amplitudes depending on the length of the bonds. We here introduce correlated AP (CAP) states, in which the amplitude product is further multiplied by factors depending on two bonds connected to a pair of sites (here nearest neighbors). While the standard AP states can describe a phase transition between an antiferromagnetic (Neel) state and a valence-bond solid (VBS) in one dimension (which we also study here), in two dimensions it cannot describe VBS order. With the CAP states, Neel-VBS transitions are realized as a function of some parameter describing the bond correlations. We here study such phase transitions of CAP wave-functions on the square lattice. We find examples of direct first-order Neel-VBS transitions, as well as cases where there is an extended U(1) spin liquid phase intervening between the Neel and VBS states. In the latter case the transitions are continuous and we extract critical exponents and address the issue of a possible emergent U(1) symmetry in the near-critical VBS. We also consider variationally optimized CAP states for the standard Heisenberg model in one and two dimensions and the J-Q model in two dimensions, with the latter including four-spin interactions (Q) in addition to the Heisenberg exchange (J) and harboring VBS order for large Q/J. The optimized CAP states lead to significantly lower variational energies than the simple AP states for these models.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑