GAP-TO-T-C RATIO AS A FUNCTION OF THE FERMI-LEVEL SHIFT

Within the framework of the BCS theory, the gap-to-T-c ratio R=2 Delta (0)/kT(c) is evaluated numerically (Delta(0) is the energy gap at T=0 and T-c is the critical temperature) for a superconductor with a van H ove singularity (vHs) in the density of states as a function of the sh ifts (delta) of the Fermi level with respect to the vHs. It is found t hat R varies asymmetrically with delta and that the variations are str ong near delta=0. Our numerical calculation shows that the largest R's occur at certain Values of delta not equal 0.