Abstract
The magnetic penetration depth (lambda) as a function of applied magnetic field and temperature in SrPt3P (T-c similar or equal to 8.4 K) was studied by means of muon-spin rotation (mu SR). The dependence of lambda(-2) on temperature suggests the existence of a single s-wave energy gap with the zero-temperature value Delta(0) = 1.55(2) meV. At the same time lambda was found to be strongly field dependent which is the characteristic feature of the nodal gap and/or multiband systems. The multiband nature of the superconducting state is further suggested by the upward curvature of the upper critical field. This apparent contradiction is resolved by SrPt3P being a particular two-band superconductor with equal gaps but different coherence lengths within the two Fermi surface sheets.