AI 中文总结
研究$^{229}\text{Th:CaF}_2$中时钟位点缺陷归属，通过热力学估计、密度泛函理论计算等方法，发现时钟活性四极分裂位点受局部氟补偿控制，为减少固态核时钟展宽提供微观基础。
AI 中文摘要
固态$^{229}\text{Th}$核时钟的性能敏感地依赖于主体晶体中钍核的微观环境。本文重新评估了$^{229}\text{Th:CaF}_2$中占主导的四极分裂钍位点，近期光谱研究将其归为钍二聚体。通过热力学估计、密度泛函理论计算和电场梯度比较，更倾向于在$\text{Ca}^{2+}$位点上孤立的$\text{Th}^{4+}$取代，由两个附近氟间隙原子电荷补偿形成$90^\circ$构型。计算还确定了一个高能混合壳间隙构型为可能的次要位点。时钟活性四极分裂位点受局部氟补偿控制而非不可避免的钍聚集。这种缺陷归属对可实现的线宽有影响，并为减少固态核时钟展宽提供微观基础。
英文摘要
The performance of solid-state $^{229}\text{Th}$ nuclear clocks depends sensitively on the microscopic environment of the thorium nucleus in the host crystal. Here we reassess the dominant quadrupole-split thorium site in $^{229}\text{Th:CaF}_2$, which has been assigned to a thorium dimer in recent spectroscopic work. Thermodynamic estimates, density functional theory calculations, and electric-field-gradient comparisons instead favor an isolated $\text{Th}^{4+}$ substitution on a $\text{Ca}^{2+}$ site charge-compensated by two nearby fluorine interstitials in a relaxed $90^\circ$ motif. The same calculation identifies a higher-energy mixed-shell interstitial motif as a plausible minor site. The clock-active quadrupole-split site is therefore controlled by local fluoride compensation rather than unavoidable thorium aggregation. This defect assignment also has implications for achievable linewidths and provides a microscopic basis for reducing broadening in solid-state nuclear clocks.
