Quasiparticle Delocalization Induced by Novel Quantum Interference in   Disordered d-Wave Superconductors
  The diagrammatic approach is applied to study quasiparticle transport properties in two-dimensional d-wave superconductors with dilute nonmagnetic impurities both in Born and in unitary limits. It is found that a novel quantum interference process gives rise to a weak-antilocalization correction to the spin conductivity, indicating the existence of extended low-energy quasiparticle states. With comimg close to unitarity and the nesting, this correction is suppressed and eventually vanishes due to the global particle-hole symmetry. 
Y.H. Yang, D.Y. Xing, M. Liu, and Y.G. Wang