Electronic structure and weak electron-phonon coupling inTaB2

Abstract

We present electronic structure calculations together with resistivity, susceptibility, and specific heat measurements for ${\mathrm{TaB}}_2$ to search for the recently contradictorily reported superconductivity and to study related normal-state properties. We ascribe the absence of superconductivity down to 1.5 K for our ${\mathrm{TaB}}_2$ samples to the generally weak electron-phonon coupling derived from comparison of the calculated and measured specific heat constants. For the $E_{2g}$ and the $B_{1g}$ $\Gamma$-point phonons, we derive from the calculated deformation potentials very small electron-phonon couplings for these modes, as opposed to the strong coupling of the $E_{2g}$ mode in ${\mathrm{MgB}}_2,$ probably responsible for its high $T_c.$ In comparison to ${\mathrm{MgB}}_2,$ we discuss the origin of the quite different features in the density of states and of the Fermi surfaces. The differences are mainly due to the strong hybridization between $\mathrm{Ta}\hspace{0.5em}5d$ and $\mathrm{B}\hspace{0.5em}2p$ states outside the hexagonal basis plane.