THE ELECTRONIC SPECIFIC-HEAT OF CUPRATE SUPERCONDUCTORS

We present the electronic specific heat coefficient gamma(T) for sever al cuprate series determined from high resolution differential measure ments. gamma(T) is consistent with Fermi statistics, a low degeneracy temperature and at most a modest low temperature mass enhancement. We show the progression of gamma(T) with hole doping for La2-ySryCuO4 and the overdoped system Tl2Ba2CuO6+delta, and demonstrate that the rapid fall in condensation energy in underdoped YBa2Cu3O6+x results from th e growth of a pseudogap in the normal state quasiparticle spectrum. We discuss the effects of Zn doping on superconducting and pseudogap cor relations in YBa2Cu3O6+x.