Dirac semimetals are materials whose electronic band structures are three-dimensional analogues of graphene, featuring electron bands with linear dispersion close to a Dirac point, forming Dirac cones. Bulk cadmium arsenide was thought to fall into this class of material, containing a single pair of Dirac cones that are protected by crystal symmetry, but experiments by Ana Akrap and colleagues suggest that the situation may be a little more complex.
Previous experiments classified the charge carriers in bulk cadmium arsenide as massless symmetry-protected Dirac fermions, which is what you'd expect for a Dirac semimetal. And although magneto-optical experiments by Akrap et al. support the idea that the carriers are massless, for certain energies, they suggest that they are actually massless Kane fermions.
Kane fermions are a type of carrier that can appear in some narrow-gap semiconductors that have conical electronic band dispersions. And although they exhibit several behaviours similar to Dirac fermions, they have quite a different origin, and are not protected by crystal symmetry. Could this material contain both massless Dirac and Kane fermions over different energy scales? The authors think so.
Rights and permissions
About this article
Cite this article
Fleet, L. A fine line. Nature Phys 12, 992 (2016). https://doi.org/10.1038/nphys3957
Published:
Issue Date:
DOI: https://doi.org/10.1038/nphys3957