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

TL;DR

This paper investigates the superconducting state in a two-dimensional d-p model using spin fluctuation theory and FLEX approximation, revealing a d_{x^2 - y^2} symmetry gap, resonance peaks, and spectral features consistent with experiments.

Contribution

It provides a detailed theoretical analysis of spin fluctuation-induced superconductivity in a d-p model, including self-consistent calculations of gap functions and spectral properties.

Findings

Gap function has d_{x^2 - y^2} symmetry and develops rapidly below T_c.

Resonance peak in spin susceptibility resembles neutron scattering observations.

Spectral density features match angle-resolved photoemission data and vary with doping.

Abstract

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 optimal- and over-doped regions of hole concentration. The gap function has a symmetry of d_{x^2 - y^2} type and develops below the transition temperature T_c more rapidly than in the BCS model. Its saturation value at the maximum is about 10 T_c. 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 YBCO. The one-particle spectral density around k=(pi,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.