Physical properties and electronic structure of La3Co and La3Ni intermetallic superconductors

Abstract

La3Co and La3Ni are reported superconductors with transition temperatures of 4.5 and 6K, respectively. Here, we reinvestigate the physical properties of these two intermetallic compounds with magnetic susceptibilityχ, specific heat Cp and electrical resistivityρ measurements down to 1.9K. Although bulk superconductivity is confirmed in La3Co, as observed previously, only a trace of it is found in La3Ni, indicating that the superconductivity in La3Ni originates from an impurity phase. Superconducting state parameters for La3Co, 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 La3Co versus La3Ni explains its larger superconducting Tc. 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 La3Co. This effect cannot be explained by the electron-phonon interaction alone. Renormalization ofγ, as well as an ∼T2behavior of the resistivity, suggests the presence of spin fluctuations in both systems.