Marginal Stability of d-Wave Superconductor: Spontaneous P and T Violation in the Presence of Magnetic Impurities

Abstract

We argue that the d _x ²−y²-wave superconductor is marginally stable in the presence of external perturbations. Subjected to the external perturbations by magnetic impurities, it develops a secondary component of the gap, complex d_xy, to maximize the coupling to impurities and lower the total energy. The secondary d_xy component exists at high temperatures and produces the full gap ∼20 Kin the single particle spectrum around each impurity apart from impurity-induced broadening. At low temperatures, the phase-ordering transition into global d _x ²−y²+id_xy state occurs.