论文标题

量子相变的紧急对称性:从骨化的量子临界点到无间隙量子旋转液体

Emergent Symmetry in Quantum Phase Transitions: From Deconfined Quantum Critical Point to Gapless Quantum Spin Liquid

论文作者

Liu, Wen-Yuan, Gong, Shou-Shu, Chen, Wei-Qiang, Gu, Zheng-Cheng

论文摘要

沮丧的磁铁中异国量子现象的出现正在迅速推动量子多体物理学的发展,从而提出了有关量子相变本性质的基本问题。在这里,我们揭示了涉及两个非凡代表性现象的紧急对称性的行为,即脱合量子临界点(DQCP)和量子旋转液体(QSL)状态。通过大尺度张量网络模拟,我们研究了一个在空间各向异性的自旋1/2平方 - 触觉挫败的反铁磁(AFM)型号,即$ j_ {1x} $ - $ j_ {1y} $ - $ j_2 $ - $ j_2 $,其中包含anisotropic $ j_ $ j_ $ j_ $ j_ $ j_ $ j_ {1y} $和下一个最近的邻居耦合$ j_2 $。对于小$ j_ {1y}/j_ {1x} $,通过调整$ j_2 $,观察到AFM和Valence Bond固相之间的直接连续过渡。(当然,不排除弱的一阶过渡的可能性,无法完全排除。我们观察到沿AFM-VBS过渡线的出现O(4)对称性,这与DQCP理论的预测一致。最令人惊讶的是,我们发现如此紧急的O(4)对称性也适用于整个QSL--VBS过渡线。这些发现从分类对称的角度揭示了QSL和DQCP之间的内在关系,并强烈限制了QSL阶段的量子场理论描述。本文介绍的相图和关键指数与对沮丧磁铁和冷原子系统的未来实验具有直接相关性。

The emergence of exotic quantum phenomena in frustrated magnets is rapidly driving the development of quantum many-body physics, raising fundamental questions on the nature of quantum phase transitions. Here we unveil the behaviour of emergent symmetry involving two extraordinarily representative phenomena, i.e., the deconfined quantum critical point (DQCP) and the quantum spin liquid (QSL) state. Via large-scale tensor network simulations, we study a spatially anisotropic spin-1/2 square-lattice frustrated antiferromagnetic (AFM) model, namely the $J_{1x}$-$J_{1y}$-$J_2$ model, which contains anisotropic nearest-neighbor couplings $J_{1x}$, $J_{1y}$ and the next nearest neighbor coupling $J_2$. For small $J_{1y}/J_{1x}$, by tuning $J_2$, a direct continuous transition between the AFM and valence bond solid phase is observed.(Of course, the possibility of weakly first order transition can not be fully excluded.) With growing $J_{1y}/J_{1x}$, a gapless QSL phase gradually emerges between the AFM and VBS phases. We observe an emergent O(4) symmetry along the AFM--VBS transition line, which is consistent with the prediction of DQCP theory. Most surprisingly, we find that such an emergent O(4) symmetry holds for the whole QSL--VBS transition line as well. These findings reveal the intrinsic relationship between the QSL and DQCP from categorical symmetry point of view, and strongly constrain the quantum field theory description of the QSL phase. The phase diagram and critical exponents presented in this paper are of direct relevance to future experiments on frustrated magnets and cold atom systems.

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