Specific heat of the cubic high-T c superconductor Ba 0·6K 0·4BiO 3

Abstract

We report magnetic susceptibility and specific heat measurements on polycrystalline samples of the 30 K superconductor Ba 0·6K 0·4BiO 3. Normal-state magnetization measurements indicate a Pauli-paramagnetic susceptibility of χ pauli = 2.3 × 10 −5 emu/mole, from which we infer a value for the density of states at the Fermi level of N(0) = 8.6 × 10 21ev −1cm. −3 Specific heat measurements performed between 1.6 K and 40 K indicate that considerable lattice softening occurs at low temperatures; the effective Debye temperature drops from ∼280 K at 35 K to ∼210 K at 4 K, implying that soft phonon modes are present in this compound. This result indicates that conventional phonon-mediated interactions may be responsible for the high transition temperature exhibited by Ba 0·6K 0·4BiO 3.