Crystal field excitations in the spin liquid candidate on a stuffed honeycomb lattice antiferromagnet:TbBO3

Quantum spin liquids (QSL) represent a highly entangled state of matter which lacks long-range magnetic order, despite strong exchange interactions between its magnetic constituents. QSLs are ideal hosts of exotic fractional quantum numbers coupled to emergent gauge fields and hold tantalizing prospects for applications in fault-tolerant quantum computing. The experimental realization of QSLs in 2D spin-lattice remains elusive in view of the presence of defects and anti-site disorder in real materials. Rare-earth based frustrated magnets offer a new route to realize the elusive QSL state with fractional magnetic excitations. Our focus is on a “stuffed honeycomb lattice” TbBO3 comprised of a honeycomb lattice with a superimposed triangular lattice formed by additional magnetic ions at the centre of each hexagon, that can support exotic quantum phenomena, including Dirac QSL. Our muon experiments down to 16 mK rule out the presence of magnetic ordering and spin freezing. Specific heat down to 100 mK shows no signature of magnetic ordering and specific heat shows power law behavior indicative of gapless spin excitations. NMR results suggest the presence of unconventional spin excitations in TbBO3. We propose to carry out inelastic neutron scattering (INS) studies to investigate the crystal field excitations to probe their energy and wave functions, which will shed light on the QSL state.

量子自旋液体（Quantum spin liquids, QSL）是一类高度纠缠的物态，尽管其磁性组分间存在强交换相互作用，却不具备长程磁序。QSL是与涌现规范场耦合的奇异分数量子数的理想载体，在容错量子计算领域拥有极具吸引力的应用前景。鉴于真实材料中普遍存在缺陷与反位无序，在二维自旋晶格中实验实现QSL至今仍难以达成。稀土基阻挫磁体为实现带有分数自旋激发的难以捉摸的QSL态提供了全新路径。本研究聚焦于"填充型蜂窝晶格"结构的TbBO3体系：该体系以蜂窝晶格为基础，每个六边形的中心额外引入磁性离子构成叠加的三角晶格，可承载包括狄拉克量子自旋液体（Dirac QSL）在内的各类奇异量子现象。我们开展的低至16毫开的μ子实验，排除了该体系存在磁有序与自旋冻结的可能。低至100毫开的比热测量未观测到磁有序的特征，且其幂律行为表明体系存在无能隙自旋激发。核磁共振（Nuclear Magnetic Resonance, NMR）结果表明，TbBO3体系中存在非常规自旋激发。我们计划开展非弹性中子散射（inelastic neutron scattering, INS）研究，对晶体场激发的能量与波函数进行探测，以此为阐明QSL态的本质提供关键依据。