CaSb2 is a bulk superconductor and a topological semimetal, making it a great platform for realizing topological superconductivity. In this work, we investigate the superconducting upper and lower critical field anisotropy using magnetic susceptibility, and study the superconducting state using muon spin-relaxation. The temperature dependence of transverse-field relaxation rate can be fitted with a single-gap model or two-gap model. 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. We conclude an s+is order parameter considering the breaking of time-reversal symmetry (TRS), which originates from competing interband interactions between the three bands of CaSb2. To explain the direction-dependent breaking of TRS we suggest loop currents developing in the plane of distorted square-net of Sb atoms.
@article{arxiv.2309.12457,
title = {Time-Reversal Symmetry Breaking Superconductivity in CaSb$_2$},
author = {M. Oudah and Y. Cai and M. V. De Toro Sanchez and J. Bannies and M. C. Aronson and K. M. Kojima and D. A. Bonn},
journal= {arXiv preprint arXiv:2309.12457},
year = {2024}
}