UNIVERSALITY IN TRANSPORT PROCESSES OF UNCONVENTIONAL SUPERCONDUCTORS

We show that some of the low temperature transport coefficients (e.g., electrical and thermal conductivities, viscosity and sound attenuatio n) are universal, i.e., independent of the impurity concentration and phase shift for specific classes of unconventional superconductors. Th e existence of a universal limit depends on the symmetry of the order parameter and is achieved at low temperatures k(B)T much less than gam ma much less than Delta(0), where gamma is the bandwidth of the impuri ty induced Andreev bound states. The density of states is finite at ze ro energy and leads to the re-appearance of the Wiedemann-Franz law de ep in the superconducting phase for k(B)T much less than gamma. Our fi ndings also show that impurity concentration studies at low temperatur es can distinguish between different order parameter symmetries.