Depth-dependent study of time-reversal symmetry-breaking in the kagome superconductor AV₃Sb₅

The breaking of time-reversal symmetry (TRS) in the normal state of kagome superconductors AV₃Sb₅ stands out as a significant feature, but its tunability is unexplored. Using low-energy muon spin rotation and local field numerical analysis, we study TRS breaking as a function of depth in single crystals of RbV₃Sb₅ (with charge order) and Cs(V_0.86Ta_0.14)₃Sb₅ (without charge order) [1]. In the bulk of RbV₃Sb₅ (33 nm from the surface), we observed an increase in the internal magnetic field width in the charge-ordered state [1,2]. Near the surface (33 nm), the muon spin relaxation rate is significantly enhanced and this effect commences at temperatures significantly higher than the onset of charge order [1]. In contrast, no similar field width enhancement was detected in Cs(V_0.86Ta_0.14)₃Sb₅, either in the bulk or near the surface. These observations indicate a strong connection between charge order and TRS breaking and suggest that TRS breaking can occur prior to long-range charge order.

[1] J.N. Graham et. al., and Z. Guguchia, Nature Communications 15, 8978 (2024).

[2] Z. Guguchia et. al., Nature Communications 14, 153 (2023).