Specific Heat of La2-xSrxCuO4 and YBa2Cu3O7 Superconductors from 1 K to Room Temperature

Abstract

The specific heat of the superconductors La_1.85Sr_0.15CuO₄ and YBa₂Cu₃O₇ was measured from 1 to 350 K. A maximum in C/T³ near 22 K indicates enhanced phonon density of states at energies ω∼11 meV. A lattice specific heat still below 3R at room temperature implies the existence of high energy phonon states at ∼50 meV or beyond. The initial Debye temperature lies in the 380–400 K range. At low temperatures, abnormal electronic contributions are seen, mainly in YBa₂Cu₃O₇. The specific heat jumps are resolved in six samples: ΔC/T_c≃14 mJ·K^-2·mole–Cu^-1 in La_1.85Sr_0.15CuO₄ and ΔC/T_c≃13 mJ·K^-2·mole–Cu^-1 in YBa₂Cu₃O₇.