CHARGE DENSITY FLUCTUATIONS AND GAP SYMMETRY IN HIGH-T_C SUPERCONDUCTORS WITH EXTENDED SADDLE-POINT FEATURES IN ELECTRON SPECTRUM

摘要

It is shown that the strong anisotropy of the one-particle electron spectrum, due to the existence of extended saddle-point features (ESPF) close to the Fermi level in the hole-type cuprates Y BCO and BSCCO, leads to the appearance of a low-frequency peak in the spectral function of the charge density fluctuations due to the presence of acoustic plasmon branch in the collective electron spectrum. The retarded anisotropic electron-plasmon interaction leads to the suppression of the static screened Coulomb repulsion for small transferred momenta and, consequently, to the effective attraction between electrons in the d_(χ~2-y~(2-)) wave channel of the Cooper pairing of current carriers. Breaking of C_(4v) symmetry in and Y BCO crystals leads to a possibility of a change of d_(χ~2-y~(2-))wave symmetry of the gap to mixed s - d gap symmetry for singlet Cooper pairs or to p-wave gap symmetry for triplet pairs.