Condensed Matter Seminars

Weyl semimetals (WSMs) have a three-dimensional (3D) bulk band structure in which the conduction and valence bands meet at discrete points, i.e. Weyl nodes. Projections of Weyl points with opposite chirality can be connected by Fermi arcs at a surface. Topological Dirac semimetals (DSMs) have 3D Dirac points which can be viewed as superimposed copies of Weyl points and are stabilized by rotational symmetry. When an external magnetic field is applied to a DSM, Dirac points can be separated into multiple Weyl points and so a WSM phase can be driven. DSMs and WSMs have received a lot of attention because of the chiral anomaly and novel magneto-transport signatures. We develop a tight-binding model based on Wannier functions directly from density functional theory (DFT) calculations for a topological DSM Na3Bi. We add spin-orbit coupling and Zeeman terms in the tight-binding model. Upon magnetic field along the rotational axis, we find that each Dirac node splits into two single Weyl nodes and two double Weyl nodes with opposite chirality, in contrast to  common belief. Our calculations also reveal an interesting evolution of Fermi-arc surface states and other topological surface states as a function of chemical potential in the presence of the external magnetic field.