Gapless quantum spin liquid, stripe, and antiferromagnetic phases in frustrated Hubbard models in two dimensions
Gapless quantum spin liquid, stripe, and antiferromagnetic phases in frustrated Hubbard models in two dimensions
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DOI：
10.1103/physrevb.74.014421
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发表时间：
2006-07-01
影响因子：
3.7
通讯作者：
Imada, Masatoshi
中科院分区：
文献类型：
--
作者：
Mizusaki, Takahiro;Imada, Masatoshi
揭示了非线性绝缘体相的独特性质，给出了正方形格子上包含对角转移t（'）的t-t（'）Hubbard模型的相图。使用路径积分重整化群方法，我们在强在位相互作用U的Mott绝缘区域中发现了次近邻转移t（'）较小的反铁磁相和t（'）较大的条纹（或共线）相。对于中等的t（'）/t，当U/t > 7时，t（'）/t近似于0.7，我们发现了一个具有2x 4结构的长周期反铁磁绝缘体相。在Mott绝缘区，我们也发现了一个量子自旋液体（换句话说，一个非线性绝缘体）相，它位于正方形晶格和各向异性三角形晶格上的t-t（'）Hubbard模型的Mott过渡到顺磁金属附近。关联电子通常会结晶成莫特绝缘体，通常具有一定的磁序，而“量子自旋液体”一直是一个长期探索的问题。我们报告的数值证据表明，一个无隙绝缘相得到稳定的莫特过渡附近的显着性能：几何阻挫晶格上的二维莫特绝缘体包含一个相位与无隙自旋激发和简并的基态在整个布里渊区的总动量。所得到的自旋重整化因子的消失表明，自旋激发不相干传播的常规阶段，其中存在磁振子在磁破碎阶段或粒子空穴激发在顺磁金属相反。它对量子自旋液体的可能图像施加了约束，并支持对非常规量子液体存在的解释。本概念是有用的，在分析各种实验结果阻挫磁体，包括有机BEDT-TTF化合物和He-3原子吸附在石墨上。
Unique features of the nonmagnetic insulator phase are revealed, and the phase diagram of the t-t(') Hubbard model containing the diagonal transfers t(') on a square lattice is presented. Using the path-integral renormalization group method, we find an antiferromagnetic phase for small next-nearest-neighbor transfer t(') and a stripe (or collinear) phase for large t(') in the Mott insulating region of the strong on-site interaction U. For intermediate t(')/t similar to 0.7 at large U/t > 7, we find a longer-period antiferromagnetic-insulator phase with 2x4 structure. In the Mott insulating region, we also find a quantum spin liquid (in other words, a nonmagnetic insulator) phase near the Mott transition to paramagnetic metals for the t-t(') Hubbard model on the square lattice as well as on the anisotropic triangular lattice. Correlated electrons often crystallize to the Mott insulator usually with some magnetic orders, whereas the "quantum spin liquid" has been a long-sought issue. We report numerical evidence that a nonmagnetic insulating phase gets stabilized near the Mott transition with remarkable properties: The two-dimensional Mott insulators on geometrically frustrated lattices contain a phase with gapless spin excitations and degeneracy of the ground state in the whole Brillouin zone of the total momentum. The obtained vanishing spin renormalization factor suggests that spin excitations do not propagate coherently in contrast to conventional phases, where there exist either magnons in symmetry-broken phases or particle-hole excitations in paramagnetic metals. It imposes a constraint on the possible pictures of quantum spin liquids and supports an interpretation for the existence of an unconventional quantum liquid. The present concept is useful in analyzing a variety of experimental results in frustrated magnets including organic BEDT-TTF compounds and He-3 atoms adsorbed on graphite.