Specific heat data of high-T c superconductors: Lattice and electronic contributions

Abstract

A high-temperature expansion for the harmonic portion of the lattice specific heat, of the form C 3Nk= ∑ ∞ n= 0 B nu -n , where u=[( T T b ) 2 + 1 ] and T b≈90 K, is used to represent the lattice specific heats of the high- T c superconductors DyBa 2Cu 3O 7 and YBa 2Cu 3O 7 near and above T c . With this expansion and published data it is possible to obtain values for the electronic specific heat coefficient (γ) of 38±3 and 40±5 mJ mol -1K -2, respectively, for DyBa 2Cu 3O 7 and YBa 2Cu 3O 7. These values for γ, when combined with the observed Δ C( T c ) at T c , are consistent with the BCS prediction that ΔC( T c )=1.43 γT c for a superconductor in the weak-coupling limit, although the shape of the specific heat anomaly for the dysprosium compound gives evidence of a fluctuation contribution.