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

TL;DR

This paper reports the identification of semi-Dirac fermions in hexagonal close-packed cadmium, revealing unique anisotropic electronic properties with potential implications for condensed matter physics.

Contribution

First principles calculations uncover semi-Dirac bands in cadmium, showing a hybridization mechanism responsible for their unique dispersion and Fermi surface shape.

Findings

Semi-Dirac bands identified at -3 eV below Fermi level

Linear dispersion persists up to Fermi level

Fermi surface cross-section matches experimental oscillation data

Abstract

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 $s$ and $p_z$ orbitals. The upper semi-Dirac band produces a lens-shaped nonellipsoidal Fermi sheet whose cross-section area has a $k$-dependence that is in excellent agreement with the experimentally measured period of Sondheimer oscillations.