Thermal conductivity measurements were performed on single crystal samples of the superconducting filled-skutterudite compounds ${\mathrm{PrOs}}_4{\mathrm{Sb}}_{12}$ and ${\mathrm{PrRu}}_4{\mathrm{Sb}}_{12}$ both as a function of temperature and transverse magnetic field. In a zero magnetic field, the low temperature electronic thermal conductivity of ${\mathrm{Pr}\mathrm{Ru}}_4{\mathrm{Sb}}_{12}$ is consistent with a fully gapped Fermi surface. For ${\mathrm{Pr}\mathrm{Os}}_4{\mathrm{Sb}}_{12}$, residual electronic conduction in the zero-temperature limit is consistent with the presence of nodes in the superconducting energy gap. The electronic thermal conductivity for both compounds shows a rapid rise at low magnetic fields. In ${\mathrm{Pr}\mathrm{Ru}}_4{\mathrm{Sb}}_{12}$, this is interpreted in terms of multiband effects. In ${\mathrm{Pr}\mathrm{Os}}_4{\mathrm{Sb}}_{12}$, we consider the Doppler shift of nodal quasiparticles and multiband effects.

• Received 21 September 2007

DOI:https://doi.org/10.1103/PhysRevLett.101.237005