标题： Zeeman分裂的Kramers双态在自旋超固体候选物Na$_{2}$BaCo(PO$_{4}$)$_{2}$中 显示英文标题

标题： Zeeman split Kramers doublets in spin-supersolid candidate Na$_{2}$BaCo(PO$_{4}$)$_{2}$

摘要： 在$_{2}$BaCo(PO$_{4}$)$_{2}$中，存在一种三角反铁磁体，在接近量子临界点的$\mu_{0}H_{c}\sim 1.6$K 附近表现出高效的绝热去磁冷却（J. Xiang $\textit{et al.}$ Nature ${\bf{625}}$, 270 (2024))，将低场磁无序相与高场完全极化的铁磁相分隔开。我们应用高分辨率背散射中子谱学在施加磁场下研究$\mu_{0}H_{c}$附近的磁激发。 在大磁场下，我们观察到铁磁涨落，这些涨落在能量上逐渐变为阻尼，低于$\mu_{0}H_{c}$时磁性是空间无序的。 我们在高场极化相中用耦合的塞曼分裂克雷默斯双态来参数化激发态，这些双态来源于自旋-轨道耦合的存在。 当磁场降低时，克雷默斯双态之间的分裂减小，如果以绝热方式降低，可以作为一种降温机制。 当施加的磁场通过$\mu_{0}H_{c}$时，激发态表征出一种纹理相，我们认为这种相在冷却方面效率不高。 在接近量子临界点的克雷默斯双态基础上构建的低温无序挫败磁体为高效的磁卡效应提供了一条途径。 显示英文摘要

摘要： Na$_{2}$BaCo(PO$_{4}$)$_{2}$ is a triangular antiferromagnet that displays highly efficient adiabatic demagnetization cooling (J. Xiang $\textit{et al.}$ Nature ${\bf{625}}$, 270 (2024)) near a quantum critical point at $\mu_{0}H_{c}\sim 1.6$ T, separating a low-field magnetically disordered from a high-field fully polarized ferromagnetic phase. We apply high resolution backscattering neutron spectroscopy in an applied field to study the magnetic excitations near $\mu_{0}H_{c}$. At large fields we observe ferromagnetic fluctuations that gradually transition to being overdamped in energy below $\mu_{0}H_{c}$ where the magnetism is spatially disordered. We parameterize the excitations in the high field polarized phase in terms of coupled Zeeman split Kramers doublets originating from the presence of spin-orbit coupling. On reducing the field, the splitting between the Kramers doublets is reduced and if done adiabatically, provides a mechanism for reducing temperature. On lowering the applied field through the $\mu_{0}H_{c}$ the excitations characterize a textured phase that we suggest is inefficient for cooling. Low temperature disordered frustrated magnets built on Kramers doublets with nearby quantum critical points provide a route for efficient magnetocalorics.