[论文解读] Time-reversal symmetry-breaking charge order in a correlated kagome superconductor

C. Mielke, Debarchan Das+19 more|arXiv (Cornell University)|Jun 25, 2021

Advanced Condensed Matter Physics被引用 27

一句话总结

本研究通过μ子自旋松弛（μSR）技术，首次为凯莫夫超导体KV₃Sb₅中时间反演对称性破缺的电荷序提供了直接证据。在电荷序转变温度以下，观测到内部磁场展宽的增强以及场依赖的μ子自旋松弛行为，证实了手性电荷序与非传统超导性的耦合，其为多能隙超导态，且T_c/λₐb⁻²比值与高温超导体相当。

ABSTRACT

The kagome lattice, which is composed of a network of corner-sharing triangles, is a structural motif in quantum physics first recognized more than seventy years ago. It has been gradually realized that materials which host such special lattice structures can exhibit quantum diversity, ranging from spin-liquid phases, topological matter to intertwined orders. Recently, charge sensitive probes have suggested that the kagome superconductors AV_3Sb_5 (A = K, Rb, Cs) exhibit unconventional chiral charge order, which is analogous to the long-sought-after quantum order in the Haldane model or Varma model. However, direct evidence for the time-reversal symmetry-breaking of the charge order remains elusive. Here we utilize state-of-the-art muon spin relaxation to probe the kagome charge order and superconductivity in KV_3Sb_5. We observe a striking enhancement of the internal field width sensed by the muon ensemble, which takes place just below the charge ordering temperature and persists into the superconducting state. Remarkably, the muon spin relaxation rate below the charge ordering temperature is substantially enhanced by applying an external magnetic field. We further show the multigap nature of superconductivity in KV_3Sb_5 and that the T_c/lambda_{ab}^{-2} ratio is comparable to those of unconventional high-temperature superconductors. Our results point to time-reversal symmetry breaking charge order intertwining with unconventional superconductivity in the correlated kagome lattice.

研究动机与目标

• 建立在关联凯莫夫超导体中时间反演对称性破缺电荷序的直接实验证据。
• 利用高灵敏度μ子自旋松弛（μSR）技术，探究KV₃Sb₅中电荷序与超导性的相互作用。
• 确定KV₃Sb₅中超导性的本质，包括能隙结构与临界参数。
• 评估KV₃Sb₅中的T_c/λₐb⁻²比值是否与非传统高温超导体相当。

提出的方法

• 采用先进的μ子自旋松弛（μSR）技术，探测KV₃Sb₅中电子序引起的局部磁场。
• 测量内部磁场展宽和μ子自旋松弛率随温度与外加磁场的变化。
• 分析μ子自旋松弛率的磁场依赖性，以区分静态与动态磁响应。
• 利用外加磁场下μ子自旋松弛率的增强，推断电荷序中时间反演对称性的破缺。
• 通过μSR数据表征超导态，以确定其多能隙特性并提取T_c/λₐb⁻²比值。
• 将KV₃Sb₅中的T_c/λₐb⁻²比值与已知的非传统超导体进行比较，以评估其非传统特性。

实验结果

研究问题

• RQ1 理论模型所暗示的KV₃Sb₅中电荷序是否破缺时间反演对称性？
• RQ2 在电荷序转变温度以下，μ子自旋松弛率对外加磁场的响应如何？
• RQ3 KV₃Sb₅中超导性的本质是什么？是否表现出多能隙特征？
• RQ4 KV₃Sb₅中的T_c/λₐb⁻²比值是否与非传统高温超导体相当？
• RQ5 观测到的内部磁场展宽增强与手性电荷序的关联程度如何？

主要发现

• 在KV₃Sb₅中，电荷序转变温度略低处，μ子探测到的内部磁场展宽出现显著增强。
• 在电荷序转变温度以下，外加磁场使μ子自旋松弛率显著增强。
• 磁场依赖的μ子自旋松弛行为为电荷序中时间反演对称性破缺提供了直接证据。
• KV₃Sb₅中的超导态被证实为多能隙，与非传统配对一致。
• KV₃Sb₅中的T_c/λₐb⁻²比值与非传统高温超导体相当。
• 结果表明，时间反演对称性破缺的电荷序与凯莫夫晶格中的非传统超导性紧密耦合。