The thermal conductivity к of underdoped YBa2Cu3Oy was measured in the T→0 limit as a function of hole concentration p across the uperconducting critical point at psc=5.0 %. The evolution of bosonic and fermionic contributions to к was tracked as the doping level evolved continuously in each of our samples. For p≤psc, we observe a T3 component in к which we attribute to the boson excitations of a phase with long-range spin or charge order. Fermionic transport, observed as a T-linear term in к which persists unaltered through psc, violates the Wiedemann-Franz law,since the electrical resistivity varies as log(1/T) and grows with decreasing p.

Thermal conductivity measurements were performed on single crystal samples of the superconducting filled-skutterudite compounds PrOs4Sb12 and PrRu4Sb12 both as a function of temperature and transverse magnetic field. In a zero magnetic field, the low temperature electronic thermal conductivity of PrRu4Sb12 is consistent with a fully gapped Fermi surface. For PrOs4Sb12, residual electronic conduction in the zerotemperature 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 PrRu4Sb12, this is interpreted in terms of multiband effects. In PrOs4Sb12, we consider the Doppler shift of nodal quasiparticles and multiband effects.