标题： SrCu₂(BO₃)₂中的两种plaquette-singlet相与Emergent SO(5)去禁闭量子临界性 显示英文标题

标题： Two Plaquette-Singlet Phases and Emergent SO(5) Deconfined Quantum Criticality in SrCu2(BO3)2

摘要： 去禁域量子临界点（DQCP）已成为量子物质物理中的一个核心开放概念，而其在Shastry-Sutherland模型中的提出随后通过实验观察到了至少一个由外加磁场诱导的最小DQC场景，该场景发生在SrCu$_2$(BO$_3$)$_2$中。然而，SrCu$_2$(BO$_3$)$_2$中plaquette-singlet相的本质仍未解决，同时DQCP对称性的识别也仍需从多种理论场景中确定。 在这里，我们进行了详细的高压$^{11}$核磁共振研究，揭示了 SrCu$_2$(BO$_3$)$_2$中同时存在完全plaquette（FP）和空plaquette（EP）相，在一个一级的压力驱动相变中以体积分数效应分离。 从EP到反铁磁（AFM）相的场致转变补充了我们之前关于FP-AFM相变的观察结果，两者都显示出去禁闭量子临界性，而近EP-AFM相变处自旋晶格弛豫率的标度，$1/T_1 \propto T^{0.6}$，表明由不同普适类支配的DQCP。 我们讨论了可能扩展Shastry-Sutherland模型的方法，以解释这些压力和场效应。 我们发现的扩展相空间要求存在SO(5)的DQCP对称性，因此我们的研究结果朝着完全理解SrCu$_2$(BO$_3$)$_2$中的去禁闭量子临界性迈出了重要一步。 显示英文摘要

摘要： The deconfined quantum critical point (DQCP) has become a central open concept in the physics of quantum matter, and its proposed presence in the Shastry-Sutherland model was followed by the experimental observation of at least a minimal DQC scenario induced by an applied magnetic field in SrCu$_2$(BO$_3$)$_2$. However, the nature of the plaquette-singlet phase in SrCu$_2$(BO$_3$)$_2$ remains unresolved, and with it the identification of the DQCP symmetry from among several theoretical scenarios. Here we perform detailed high-pressure $^{11}$B NMR studies to reveal the presence of both the full-plaquette (FP) and empty-plaquette (EP) phases in SrCu$_2$(BO$_3$)$_2$, phase-separated at a first-order, pressure-driven transition with a volume-fraction effect. The field-driven transition from the EP to the antiferromagnetic (AFM) phase complements our previous observations of the FP--AFM transition, with both showing deconfined quantum criticality, while the scaling of the spin-lattice relaxation rate near the EP--AFM transition, $1/T_1 \propto T^{0.6}$, suggests a DQCP governed by a different universality class. We discuss possible extensions to the Shastry-Sutherland model that account for these pressure and field effects. The expanded phase space we discover mandates an SO(5) DQCP symmetry, and hence our results take an important step towards a complete understanding of deconfined quantum criticality in SrCu$_2$(BO$_3$)$_2$.