  We report the discovery of a family of ternary platinum phosphides APt3P (A =
Ca, Sr and La), which crystallize in an antiperovskite-based structure closely
related to that of the heavy fermion superconductor CePt3Si. All three
phosphides showed superconductivity at low temperatures and the highest
critical temperature Tc = 8.4 K was observed for SrPt3P. The analysis of
specific heat C(T) for SrPt3P shows clear evidence for very strong coupling
s-wave superconductivity with a large ratio between superconducting gap D0 and
Tc, 2D0/kBTc ~ 5, and the presence of low-energy phonons. The presence of
multiple Fermi surface pockets was inferred from the nonlinear magnetic field
dependence of Hall resistivity, which we argue might play a role in realizing
the strong coupling of charge carriers with the low lying phonons.
