Multiband superconductivity and penetration depth in PrOs$_{4}$Sb$_{12}$*

The penetration depth lambda in the filled-skutterudite heavy-fermion superconductor PrOs$_4$Sb$_{12}$ has been measured using transverse-field muon spin rotation. It is found to be temperature-independent at low temperatures, consistent with a nonzero gap for quasiparticle excitations. In contrast, zero-field radiofrequency inductive measurements yield a stronger temperature dependence of lambda, indicative of point nodes in the gap. A $\sim$10\% discrepancy is found at intermediate temperatures. This seems likely to be due to multiband superconductivity in this compound, recently found from thermal conductivity measurements. A sufficiently large difference between gaps would render the field distribution in the vortex controlled exclusively by the larger gap band, whereas all bands would participate in zero field.