ROLE OF ORTHORHOMBIC DISTORTION, 2ND-NEAREST-NEIGHBOR HOPPING, AND COULOMB REPULSION ON THE SUPERCONDUCTING TRANSITION-TEMPERATURE AND ISOTOPE-SHIFT EXPONENT

The effect of orthorhombic distortion, second-nearest-neighbor hopping, and Coulomb repulsion on the superconducting transition temperature (Tc) and the isotope-shift exponent (α) are studied within the van Hove singularity scenario. The orthorhombic distortion decreases the maximum value of Tc (Tcm) and increases the minimum value of α (αmin). With increasing second-nearest-neighbor hopping Tcm rises sharply while α remains almost unaltered. Coulomb repulsion suppresses both Tc and α. A study of Δ(T)/Δ(0) and 2Δ(0)/KBTc reveals that the ratios do not depend on the orthorhombic distortion and second-nearest-neighbor hopping parameter. © 1995 The American Physical Society.