Magnetic-flux entry into aligned Pb-Cd eutectic composites in the proximity-effect regime

The thermal conductivity of Pb-Cd lamellar eutectic composites was measured as a function of the applied magnetic field from 1 to 8 K. The directions of heat flow and magnetic field were parallel to each other and to the lamellae. For samples of large periodicity, the data are consistent with the theory of Dobrosavljevic and de Gennes in which the magnetic flux enters the Cd lamellae in the form of quantized vortices. The resulting decrease in thermal conductivity is interpreted in terms of Andreev scattering of quasiparticles at the pair-potential barrier of a vortex. These results are compared with similar measurements by Deutscher et al. on vapor-deposited Pb-Ag-Pb films