Nematic superconductivity in the topological semimetal CaSn3

The superconducting behavior of the topological semimetal CaSn3 was investigated by means of magnetotransport and muon spectroscopy (?SR) measurements, both providing strong evidence of nematic behavior. Magnetotransport detects an anisotropic upper critical field, characterized by a twofold symmetry about C4 axis, thus breaking the rotational symmetry of the underlying cubic lattice. Transverse-field ?SR data support such picture, with the muon depolarization rate depending strongly on the magnetic field direction, here applied along the [110] or [001] crystal directions. In the former case, the absence of any additional muon depolarization suggests an unconventional vortex lattice. In the latter case, a vortex lattice encompassing a sample volume of at least 52% indicates the bulk nature of CaSn3 superconductivity. The resulting superfluid density in the (001) planes shows a gapped low-temperature behavior, with a superconducting gap value ?(0)?0.61(7) meV. Additional zero-field ?SR results indicate that the superconducting state is time-reversal invariant. This fact and the breaking of rotational symmetry in a fully gapped superconductor are consistent with an unconventional pairing state in a multidimensional representation, thus making CaSn3 an important example of nematic superconductor.