Wave packets in Honeycomb Structures and Two-Dimensional Dirac Equations
  In a recent article [10], the authors proved that the non-relativistic Schr\"odinger operator with a generic honeycomb lattice potential has conical (Dirac) points in its dispersion surfaces. These conical points occur for quasi-momenta, which are located at the vertices of the Brillouin zone, a regular hexagon. In this paper, we study the time-evolution of wave-packets, which are spectrally concentrated near such conical points. We prove that the large, but finite, time dynamics is governed by the two-dimensional Dirac equations. 
Charles L. Fefferman and Michael I. Weinstein
math-ph cond-mat.mes-hall math.AP math.MP quant-ph