Spectral and transport properties of d -wave superconductors with strong impurities

One of the remarkable features of disordered d-wave superconductors is strong sensitivity of long range properties to the microscopic realization of the disorder potential. Particularly rich phenomenology is observed for the\char22{}experimentally relevant\char22{}case of dilute distributions of isolated impurity centers. Building on earlier diagrammatic analyses, the present paper derives and analyzes a low energy effective field theory of this system. Specifically, the results of previous diagrammatic T-matrix approaches are extended into the perturbatively inaccessible low energy regimes, and the long range (thermal) transport behavior of the system is discussed. It turns out that in the extreme case of a half-filled tight binding band and infinitely strong impurities (impurities at the unitary limit), the system is in a delocalized phase.