NONZERO FERMI-LEVEL DENSITY-OF-STATES FOR A DISORDERED D-WAVE SUPERCONDUCTOR IN 2 DIMENSIONS

In 3D, arbitrarily weak disorder in superconductors with line nodes gi ves rise to a nonzero Fermi level density of states N(0), leading to c haracteristic low-temperature thermodynamics similar to that observed in cuprate and heavy-fermion systems. In a strictly 2D model, possibly appropriate for the cuprates, it has been argued that N(0) vanishes. We perform an exact calculation for a 2D d-wave superconductor with Lo rentzian disorder and find a nonzero N(0). For other continuous distri butions we obtain a nonzero lower bound for N(0). We discuss the reaso ns for this discrepancy.