Rotational symmetry breaking in the upper critical field of topological superconductor candidate CaSn₃

Electronic nematicity is a quantum analogue to liquid crystals, breaking the rotational symmetry, but preserving the translational symmetry. The electronic nematic states emerge not only in strongly correlated systems, including quantum Hall liquids, high temperature cuprate and iron-based superconductors, and heavy fermion compounds [1], but also in weakly correlated systems, such as the superconducting states in doped-topological insulators known as nematic superconductivity [2]. Closely correlated with the topological nature, the nematic superconductivity in topological materials has attracted great interest. Here, we report systematic studies of the upper critical field of topological superconductor candidate CaSn₃, forming a cubic structure with point group Oh. We reveal two-fold symmetry in the anisotropy of upper critical field, breaking the underlying lattice structure. Similar to doped-topological insulator M_xBi₂Se₃ (M=Sr, Cu and Nb), the rotational symmetry breaking indicates the realization of nematic superconductivity in CaSn₃. We will discuss the possible superconducting pairing state stabilized in this system.
[1] E. Fradkin et al., Annu. Rev. Condens. Matter Phys. 1, 153 (2010).
[2] L. Fu, Phys. Rev. B 90, 100509 (2014).