Theory of Spin Fluctuation-Induced Superconductivity Based on a d-p Model II —Superconducting State—

The superconducting state of a two-dimensional d-p model is studied from the spin fluctuation point of view by using a strong coupling theory. The fluctuation exchange (FLEX) approximatoin is employed to calculate the spin fluctuations and the superconducting gap functions self-consistently in the optimaland over-doped regions of hole concentration. The gap function has a symmetry of dx2−y2 type and develops below the transition temperature Tc more rapidly than in the BCS model. Its saturation value at the maximum is about 10kBTc. When the spin fluctuation-induced superconductivity is well stabilized at low temperatures in the optimal regime, the imaginary part of the antiferromagnetic spin susceptibility shows a very sharp resonance peak reminiscent of the 41 meV peak observed in the neutron scattering experiment on YBa2Cu3O7. The one-particle spectral density around k = (π, 0) shows sharp quasi-particle peaks followed by dip and hump structures bearing resemblance to the features observed in the angle-resolved photoemission experiment. With increasing doping concentration these features gradually disappear.