Terahertz relativistic spatial solitons in doped graphene metamaterials
  We propose an electrically tunable graphene-based metamaterial showing a large nonlinear optical response at THz frequencies, which we calculate analytically for the first time to our knowledge and arises from the intraband current. The structure sustains a novel type of stable two-dimensional spatial solitary wave, a relativistic version of the Townes soliton. These results can be also applied to any material exhibiting a conical dispersion with massless Dirac fermions. 
Haiming Dong, Claudio Conti, Fabio Biancalana
physics.optics cond-mat.other nlin.PS quant-ph