Marginal Stability of d -Wave Superconductor: Spontaneous P and T Violation in the Presence of Magnetic Impurities
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 dxy, to maximize the coupling to impurities and lower the total energy. The secondary dxy 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+idxy state occurs.