Physical properties and electronic structure of La3Co and La3Ni intermetallic superconductors.

La 3 Co and La 3 Ni are reported superconductors with transition temperatures of 4.5 and 6 K, respectively. Here, we reinvestigate the physical properties of these two intermetallic compounds with magnetic susceptibility χ, specific heat C p and electrical resistivity ρ measurements down to 1.9 K. Although bulk superconductivity is confirmed in La 3 Co, as observed previously, only a trace of it is found in La 3 Ni, indicating that the superconductivity in La 3 Ni originates from an impurity phase. Superconducting state parameters for La 3 Co, including lower and upper critical fields and the superconducting gap, are estimated. Results of the theoretical calculations of the electronic structure for both materials are also presented, and comparison of the Fermi level location in La 3 Co versus La 3 Ni explains its larger superconducting T c . A major discrepancy between band structure calculations and the experimentally measured Sommerfeld coefficient is found. The measured electronic density of states is about 2.5 times larger than the theoretical value for La 3 Co. This effect cannot be explained by the electron-phonon interaction alone. Renormalization of γ, as well as an ∼T 2 behavior of the resistivity, suggests the presence of spin fluctuations in both systems. [ABSTRACT FROM AUTHOR]