Critical Field Anisotropy and Muon Spin Relaxation Study of Superconducting Dirac-Semimetal CaSb₂

CaSb₂ has been identified as a topological semimetal [1] and a bulk superconductor[2,3], which makes it a great platform for realizing topological superconductivity. We investigate the superconducting upper and lower critical field anisotropy using magnetic susceptibility on single crystals [4], and study the superconducting state using muon spin-relaxation. The temperature dependence of transverse-field relaxation can be fitted with a single-gap model or two-gap model [4], consistent with previous tunnel-diode oscillator measurements. Zero-field relaxation shows little temperature dependence when the muon-spin is parallel to the c∗-axis, while an increase in relaxation appears below 1~K when the muon-spin is parallel to the ab-plane. This may be related to a second superconducting phase appearing at low temperature below the bulk T_c. However, we find no discernible anomaly in μ₀H_c1(0) around this temperature as has been seen in other superconductors with secondary superconducting states that appear at lower temperatures.

[1] K. Funada, et al., JPSJ, 88, 044711 (2019).

[2] A. Ikeda, et al., PRM, 4, 041801(R) (2020).

[3] M. Oudah, et al., PRB, 105, 184504 (2022).

[4] M. Oudah, et al., arXiv:2309.12457 (2023).