Specific heat evidence for a large energy gap in YBCO

Abstract

Using a high precision differential calorimeter we have determined the temperature dependence of the electronic specific heat coefficient γ s (T) of superconducting YBa 2 Cu 3 O 7 (YBCO) from 1.5K to above the transition temperature T c ∼90K. γ s (T) is shown to have a constant plus an exponential term, the latter corresponding to a large energy gap Δ for excitations with 2Δ(0)/kT c = 6.0+.5. The normal state value γ n = 16±3 mJ/mole.K 2 and the thermodynamic critical field H c (0) = 8.15±.05 kOe.