Abstract

Dirac and Weyl semimetals are three-dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry. As three-dimensional analogs of graphene, they have generated much recent interest. They possess linear band dispersion in all three dimensions (in k-space) around symmetry protected crossing points of the valence and conduction bands (Dirac points). Because of the nontrivial topology of the energy bands and the existence of Dirac points these materials possess fundamentally very interesting transport and magnetic properties. Cd3As2 is predicted to be a symmetry-protected topological semimetal with a single pair of three-dimensional (3D) Dirac points in the bulk and unusual Fermi arcs on the surfaces. It can be driven into a topological insulator and a Weyl semimetal state by symmetry breaking. The nodal loop ZrSiS semimetal is regarded as a promising new material with a very wide energy window (0-2 eV) of linear Dirac dispersion and interesting non-symmorphic symmetry protected surface states. We have successfully synthesized monocrystals of various 3D Dirac and Weyl semimetals: Pb0.83Sn0.17Se, Cd3As2, TaP, ZrSiS, and measured their transport and magnetic properties. In this talk I will present detailed study of the transport and magnetic properties of these Dirac and Weyl semimetal monocrystals with reduced charge concentration. The de Haas-van Alphen (dHvA) and the Shubnikov-de Haas (SdH) oscillations are used to probe the properties of the Fermi surface in these single crystals.