Seifert Urban F P, Willsher Josef, Drescher Markus, Pollmann Frank, Knolle Johannes
Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA, USA.
Institute for Theoretical Physics, University of Cologne, Cologne, Germany.
Nat Commun. 2024 Aug 19;15(1):7110. doi: 10.1038/s41467-024-51367-w.
Quantum fluctuations can inhibit long-range ordering in frustrated magnets and potentially lead to quantum spin liquid (QSL) phases. A prime example are gapless QSLs with emergent U(1) gauge fields, which have been understood to be described in terms of quantum electrodynamics in 2+1 dimension (QED). Despite several promising candidate materials, however, a complicating factor for their realisation is the presence of other degrees of freedom. In particular lattice distortions can act to relieve magnetic frustration, precipitating conventionally ordered states. In this work, we use field-theoretic arguments as well as extensive numerical simulations to show that the U(1) Dirac QSL on the triangular and kagome lattices exhibits a weak-coupling instability due to the coupling of monopoles of the emergent gauge field to lattice distortions, leading to valence-bond solid ordering. This generalises the spin-Peierls instability of one-dimensional quantum critical spin chains to two-dimensional algebraic QSLs. We study static distortions as well as quantum-mechanical phonons. Even in regimes where the QSL is stable, the singular spin-lattice coupling leads to marked temperature-dependent corrections to the phonon spectrum, which provide salient experimental signatures of spin fractionalisation. We discuss the coupling of QSLs to the lattice as a general tool for their discovery and characterisation.
量子涨落能够抑制受挫磁体中的长程有序，并有可能导致量子自旋液体（QSL）相。一个典型例子是具有涌现U(1)规范场的无隙QSL，人们已经认识到它可以用2 + 1维量子电动力学（QED）来描述。然而，尽管有几种很有前景的候选材料，但实现它们的一个复杂因素是存在其他自由度。特别是晶格畸变会起到缓解磁挫折的作用，从而导致传统的有序状态。在这项工作中，我们用场论论证以及广泛的数值模拟表明，三角晶格和 Kagome 晶格上的U(1)狄拉克QSL由于涌现规范场的单极子与晶格畸变的耦合而表现出弱耦合不稳定性，从而导致价键固体有序。这将一维量子临界自旋链的自旋 - 皮尔斯不稳定性推广到了二维代数QSL。我们研究了静态畸变以及量子力学声子。即使在QSL稳定的区域，奇异的自旋 - 晶格耦合也会导致声子谱出现明显的温度依赖修正，这为自旋分数化提供了显著的实验特征。我们将QSL与晶格的耦合作为发现和表征它们的一种通用工具进行了讨论。
