Frequency-dependent polarizability, plasmons, and screening in the 2D pseudospin-1 dice lattice

摘要

We calculate the dynamic polarizability under the random phase approximationfor the dice lattice. This two-dimensional system gives rise to massless Diracfermions with pseudospin-1 in the low-energy quantum excitation spectrum,providing a Dirac-cone plus flat-band dispersion. Due to the presence of theflat band, the polarizability shows key differences to that of graphene (thepseudospin-1/2 Dirac material). We find that the plasmon branch is pinched into a single point, $\omega_p=q=\mu$, independent of the background dielectricconstant. Finally, screening effects are discussed with regard to impurities.