Plasmon in Nonsymmorphic Dirac semimetals

Abstract

We consider the effect of the Coulomb interaction in a nonsymmorphic Dirac semimetal, leading to collective charge oscillation modes (plasmons), focusing on the model originally predicted by Young and Kane [Phys. Rev. Lett. 115, 126803 (2015)]. We model the system in a two-dimensional squarelattice and evaluate the density-density correlation function within the random-phase approximation (RPA) in presence of the Coulomb interaction. The non-interacting band-structure consists of three band-touching points, near which the electronic states follow Dirac equations. Two of these Dirac nodes, at the momentum points X1 and X2 are anisotropic, i.e, disperses with different velocities in different directions, whereas the third Dirac point at M is isotropic. Interestingly we find that, the system of these three Dirac nodes hold a single low-energy plasmon mode, within its particlehole gap, that disperses in isotropic manner, in the case when the nodes at X1 and X2 are related by symmetry. We also show this analytically using a long-wavelength approximation. We discuss effects of perturbations that can give rise to anisotropic plasmon dispersions and comment on possible experimental observation of our prediction.