  The superconducting behavior of the topological semimetal CaSn$_{3}$ was
investigated by means of magnetotransport and muon spectroscopy $\mu$SR
measurements, both providing strong evidence of nematic behavior.
Magnetotransport detects an anisotropic upper critical field, characterized by
a twofold symmetry about $C_{4}$ axis, thus breaking the rotational symmetry of
the underlying cubic lattice. Transverse-field $\mu$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
CaSn$_{3}$ superconductivity. The resulting superfluid density in the (001)
planes shows a gapped low-temperature behavior, with a superconducting gap
value $\Delta(0)\simeq 0.61(7)$ meV. Additional zero-field $\mu$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 multi-dimensional
representation, thus making CaSn$_{3}$ an important example of nematic
superconductor.
