The electronic thermal conductivity of superconductors with paramagnetic impurities

We have measured the thermal conductivitiesKs in the superconducting state andKn in the normal state of (La1−x REx) Al2 single crystals (RE: Gd, Ce;x≦0.005) between 0.4 and 8 K. The lattice conductivity is small in the superconducting state above 0.5Tc and in the normal state and is independent of annealing. Annealing does, however, strongly depress the ratioKse/Kne of the electronic thermal conductivities. We also report on a theory of the electronic thermal conductivity which describes the experimental results quantitatively. Interaction effects between impurities show up for the samples with the highest RE-concentration.