Electronic Band Structure and Fermi Surface of Heavy-Fermion Neptunium Superconductor NpPd₅Al₂

Abstract

Electronic band structure calculations were carried out for a new neptunium superconductor NpPd₅Al₂ using a relativistic linear-augmented plane wave method within a local density approximation. The Fermi energy in the band structure is found to be located just on the 5f-bands of the j=5⁄2 state with the extremely narrow band width and therefore the theoretical electronic specific heat coefficient γ_b is extremely large, being γ_b=74.0 mJ/(K²·mol), which is compared to γ=390 mJ/(K²·mol) estimated experimentally. NpPd₅Al₂ is an uncompensated metal. The main electron Fermi surface corresponds to a doughnut-like flat Fermi surface centered at the Γ point which is connected with cylindrical Fermi surfaces elongated along the X–W–P line.