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Valence Bonds in Random Quantum Magnets: Theory and Application to YbMgGaO 4

机译：随机量子磁铁中的价键：理论与应用于YBMGGAO 4

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We analyze the effect of quenched disorder on spin- 1 / 2 quantum magnets in which magnetic frustration promotes the formation of local singlets. Our results include a theory for 2D valence-bond solids subject to weak bond randomness, as well as extensions to stronger disorder regimes where we make connections with quantum spin liquids. We find, on various lattices, that the destruction of a valence-bond solid phase by weak quenched disorder leads inevitably to the nucleation of topological defects carrying spin- 1 / 2 moments. This renormalizes the lattice into a strongly random spin network with interesting low-energy excitations. Similarly, when short-ranged valence bonds would be pinned by stronger disorder, we find that this putative glass is unstable to defects that carry spin- 1 / 2 magnetic moments, and whose residual interactions decide the ultimate low-energy fate. Motivated by these results we conjecture Lieb-Schultz-Mattis-like restrictions on ground states for disordered magnets with spin 1 / 2 per statistical unit cell. These conjectures are supported by an argument for 1D spin chains. We apply insights from this study to the phenomenology of YbMgGaO 4 , a recently discovered triangular lattice spin- 1 / 2 insulator which was proposed to be a quantum spin liquid. We instead explore a description based on the present theory. Experimental signatures, including unusual specific heat, thermal conductivity, and dynamical structure factor, and their behavior in a magnetic field, are predicted from the theory, and compare favorably with existing measurements on YbMgGaO 4 and related materials.
机译：我们分析淬火紊乱对旋转1/2量子磁体的影响，其中磁挫伤促进了局部单曲的形成。我们的结果包括弱粘合随机性的2D价键固体的理论，以及延伸的延长，以与量子旋转液体连接的更强的障碍制度。我们在各种格子上发现，通过弱淬火病症破坏价键固相的破坏，不可避免地导致携带旋转1/2时刻的拓扑缺陷的成核。这使得晶格重整为具有有趣的低能量激励的强烈旋转网络。同样，当短途无紊乱牢固地固定短途的价键时，我们发现该推定的玻璃对携带旋转1/2磁矩的缺陷是不稳定的，并且其残留相互作用决定了最终的低能量命运。通过这些结果激励，我们向地面状态推测LieB-Schultz-Mattis的限制，用于每种统计单元细胞旋转1/2的旋转磁体。这些猜想由1D旋转链的参数支持。我们将本研究的见解施加到Ybmggao 4的现象学，最近发现的三角形格子旋转-1 / 2绝缘体，其提出是量子旋转液体。我们反思了基于本理论的描述。在理论上预测了实验鉴定，包括不寻常的特异性热，导热性和动态结构因子，以及它们在磁场中的行为，并比较ybmggao 4和相关材料的现有测量。

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