Deep-lying semi-Dirac fermions in hexagonal close-packed cadmium

Semi-Dirac fermions are massless in one direction and massive in the perpendicular directions. Such quasiparticles have been proposed in various contexts in condensed matter. Using first principles calculations, we identify a pair of semi-Dirac bands anti-crossing at -3 eV below the Fermi level in the electronic structure of hexagonal close-packed cadmium. The linear out-of-plane dispersion is kept up to the Fermi level. We demonstrate that the dichotomy between the linear and quadratic dispersions is driven by an orientation-sensitive hybridization between the<i>s</i>and<i>p_z</i>orbitals. The upper semi-Dirac band produces a lens-shaped nonellipsoidal Fermi sheet whose cross-section area has a<i>k</i>-dependence that is in excellent agreement with the experimentally measured period of Sondheimer oscillations.