Abstract
A three-dimensional (3D) Dirac semimetal (SM) is the 3D analogue of graphene having linear energy dispersion around Fermi points. Owing to the nontrivial topology of electronic wave functions, the 3D Dirac SM shows nontrivial physical properties and hosts various exotic quantum states such as Weyl SMs and topological insulators under proper external conditions. There are several kinds of Dirac SMs proposed theoretically and partly confirmed experimentally, but its unified picture is still missing. In this talk, we propose a general framework to classify stable 3D Dirac SMs in systems having the time-reversal, inversion and uniaxial rotational symmetries. We show that there are two distinct classes of 3D Dirac SMs. In one class, the Dirac SM possesses a single Dirac point at a time-reversal invariant momentum on the rotation axis. Whereas the other class of Dirac SMs has a pair of Dirac points created by band inversion, and carries a quantized topological invariant. Moreover, we show that a quantized topological charge can be assigned to each Dirac point which ensures the stability of 3D Dirac semimetals.
Coffee and tea will be served 20 minutes prior to the seminar.