AI 中文总结
该研究测量YBCO共面波导谐振器的微波响应，发现其低温异常特性无法用传统双能级系统模型解释，提出可能与缺陷局域磁矩或安德烈夫束缚态的顺磁响应有关。
AI 中文摘要
我们报道了基于YBa₂Cu₃O₇₋δ（YBCO）薄膜制备的共面波导（CPW）谐振器在约70 mK至40 K温度范围内的微波响应。这些谐振器在70 mK时的内部品质因数Qᵢ范围为4×10³至10⁴，在6 K附近升高至约8×10³至1.2×10⁴的最大值。低温下，Qᵢ和谐振频率的分数偏移Δfᵣ/fᵣ均随温度升高而增大，其行为定性上与通常和双能级系统（TLS）缺陷相关的特性相似。然而，两者的响应在由谐振器频率设定的温度标度上均未饱和，且损耗未表现出可观测的微波功率依赖性。我们表明，低温下的频率回升可更好地用与缺陷诱导的局域磁矩或安德烈夫束缚态相关的额外顺磁响应来描述，而低温损耗遵循近似对数的温度依赖性，其微观起源仍未解决。这些测量确立了图案化YBCO谐振器的毫开尔文性能，并表明其低温响应无法仅在传统TLS框架内得到理解。
英文摘要
We report the microwave response of coplanar-waveguide (CPW) resonators fabricated from $\mathrm{YBa_2Cu_3O_{7-δ}}$ (YBCO) thin films over temperatures from approximately $70~\mathrm{mK}$ to $40~\mathrm{K}$. The resonators exhibit internal quality factors $Q_\mathrm{i}$ in the range of $4\times10^3$ to $10^4$ at 70 mK, which increase to a maximum of approximately $8\times10^3$ to $1.2\times10^4$ near $6~\mathrm{K}$. At low temperatures, both $Q_\mathrm{i}$ and the fractional shift of the resonance frequency $Δf_\mathrm{r}/f_\mathrm{r}$ increases with temperature, qualitatively resembling behavior commonly associated with two-level-system (TLS) defects. However, neither response saturates on the temperature scale set by the resonator frequency, and the loss exhibits no observable microwave-power dependence. We show that low-temperature frequency upturn may be better described by an additional paramagnetic response associated with defect-induced local moments or Andreev bound states, while the low-temperature loss follows an approximately logarithmic temperature dependence whose microscopic origin remains unresolved. These measurements establish the millikelvin performance of patterned YBCO resonators and show that their low-temperature response cannot be understood within the conventional TLS framework alone.
Comments8 pages, 5 figures
