AI 中文总结
本研究通过最高24 T的强场比热测量，发现α-RuCl₃中的Kitaev量子自旋液体在~15 T的交叉点后仍存续于非微扰区域，直至磁化饱和值的90%处才向自旋极化态转变。
AI 中文摘要
Kitaev量子自旋液体（KQSL）拥有由巡游Majorana准粒子和带隙Z₂通量（visons）描述的分数化激发，为研究涌现拓扑物质提供了平台。然而这类状态能否在强磁场下存续仍是未解决的问题。层状蜂窝磁体α-RuCl₃是候选材料：~7 T的面内磁场可抑制反铁磁序，诱导出呈现Majorana激发特征的量子无序相，包括反常热霍尔效应和与磁场角度相关的比热。在更高场下，磁化强度趋近饱和，暗示向自旋极化态转变，但两种极限间的微观演化仍未明确。本研究报告了最高24 T的强场比热测量结果，发现在μ₀H*≈15 T处存在明显的交叉点，超出该点后微扰Kitaev描述失效。在H*以上，比热特有的六重角调制消失，激发带隙偏离预测的H³标度；同时带隙随磁场增大而减小，面内磁化各向异性持续存在至~24 T，这与平凡自旋极化态形成鲜明对比，表明即使在磁化强度饱和值的~90%处，KQSL的特征仍得以保留。这些结果揭示α-RuCl₃中的KQSL远超出微扰范围，在Majorana和vison能标合并的非微扰区域存续，最终才让位于自旋极化。该热力学路径为理解分数化相在强磁场下的演化提供了基础。
英文摘要
Kitaev quantum spin liquids (KQSLs) host fractionalized excitations described by itinerant Majorana quasiparticles and gapped $Z_2$ fluxes (visons), providing a platform for emergent topological matter. Whether such a state survives under strong magnetic fields, however, remains an open question. The layered honeycomb magnet $α$-RuCl$_3$ is a leading candidate material: an in-plane field of $\sim$ 7 T suppresses antiferromagnetic order and induces a quantum-disordered phase exhibiting signatures consistent with Majorana excitations, including an anomalous thermal Hall effect and field-angle-dependent specific heat. At higher fields, the magnetization approaches saturation, suggesting a transition to a spin-polarized state, yet the microscopic evolution between these limits remains unresolved. Here we report high-field specific heat measurements up to 24 T that reveal a distinct crossover at $μ_0H^*\approx$15 T, beyond which the perturbative Kitaev description breaks down. Above $H^*$, the characteristic six-fold angular modulation of the specific heat collapses and the excitation gap deviates from the predicted $H^3$ scaling. Meanwhile, the gap decreases with increasing field and the in-plane magnetization anisotropy persists up to $\sim$ 24 T, both in sharp contrast to a trivial spin-polarized state, indicating that KQSL signatures are preserved even at $\sim$ 90 % of magnetization saturation. These results reveal that the KQSL in $α$-RuCl$_3$ extends well beyond the perturbative window, persisting as a nonperturbative regime in which the Majorana and vison energy scales merge, before eventually giving way to spin polarization. This thermodynamic roadmap provides a basis for understanding how fractionalized phases evolve under strong magnetic fields.
Comments10 pages, 6 figures
