Electronic structure and weak electron-phonon coupling in TaB 2

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 ${B}_{1g}$ $\ensuremath{\Gamma}$-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 $\mathrm{Ta} 5d$ and $\mathrm{B} 2p$ states outside the hexagonal basis plane.