Transport in Unconventional Superconductors

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9600105 Hirschfeld Theoretical research designed to aid in the identification of the pairing state of the copper oxide and heavy fermion superconductors and the development of a practical theory of transport below the critical temperature will be conducted. The primary focus will be on the effect of disorder and magnetic field on low-temperature properties. Previous theory has provided a good description of experimental results reflecting the disorder-dependent quasiparticle density of states in terms of a dirty d-wave picture. Calculations of the scattering amplitude for a d-wave order parameter will be performed, including self-consistent off diagonal scattering, in an attempt to address inadequacies of the simplest models of this kind in the description of transport properties. Such corrections to the theory may not be ignored and are likely to introduce qualitatively new physics. At all stages, comparisons will be made with anisotropic s-wave states to search for qualitative differences. Several instances in the theory where deviations from the usual model spherical or ellipsoidal Fermi surface can lead to qualitatively new effects will be investigated. Examples include the breaking of spurious isotropy of transport coefficients in the E2u pairing scenario for UPt3 by hexagonal anisotropy, and the creation of matrix elements for off-diagonal scattering due to orthorhombicity in the d wave model for YBCO and BSCCO. Finally, transport properties of unconventional superconductors in a finite magnetic field will be calculated, accounting for the most significant unusual features of the unconventional vortex lattice, such as the large density of unbound quasiparticle excitations over the entire vortex. This will involve a careful analysis of the scattering cross-section for electrons from a single d-wave vortex. A semimicroscopic transport theory including impurity scattering will then be formulated and applied to measurements of thermal and electric al conductivities and Hall coefficients in the superconducting state. %%% Theoretical research will be conducted on various aspects of superconductivity in the high temperature superconductors and the so-called heavy-fermion superconductors. In particular, studies will be made of transport properties and on the effects of disorder and magnetic fields on superconducting state properties. ***