  By employing a series of experimental techniques, we provide clear evidence
that CaPtAs represents a rare example of a noncentrosymmetric superconductor
which simultaneously exhibits nodes in the superconducting gap and broken
time-reversal symmetry (TRS) in its superconducting state (below $T_c$
$\approx$ 1.5 K). Unlike in fully-gapped superconductors, the magnetic
penetration depth $\lambda(T)$ does not saturate at low temperatures, but
instead it shows a $T^2$-dependence, characteristic of gap nodes. Both the
superfluid density and the electronic specific heat are best described by a
two-gap model comprising of a nodeless gap and a gap with nodes, rather than by
single-band models. At the same time, zero-field muon-spin spectra exhibit
increased relaxation rates below the onset of superconductivity, implying that
TRS is broken in the superconducting state of CaPtAs, hence indicating its
unconventional nature. Our observations suggest CaPtAs to be a new remarkable
material which links two apparently disparate classes, that of TRS-breaking
correlated magnetic superconductors with nodal gaps and the weakly-correlated
noncentrosymmetric superconductors with broken TRS, normally exhibiting only a
fully-gapped behavior.
