SUPERCONDUCTING UPPER CRITICAL-FIELD NEAR A 2D VANHOVE SINGULARITY

The superconducting upper critical field H-c2(T) of a two dimensional BCS superconductor is calculated in the vicinity of a van-Hove singula rity. The zero temperature upper critical field is strongly enhanced a t weak coupling when the Fermi contour coincides with van-Hove points, scaling as H-c2(0) proportional to T-c(root 2) compared to the usual result H-c2(0) proportional to T-c(2). The result can be interpreted i n terms of the unusual Fermi liquid decay of normal state pair correla tions in the vicinity of a van-Hove point. Copyright (C) 1996 Elsevier Science Ltd