Trapping photon-dressed Dirac electrons in a quantum dot studied by   coherent two dimensional photon echo spectroscopy
  We study the localization of dressed Dirac electrons in a cylindrical quantum dot (QD) formed on monolayer and bilayer graphene by spatially different potential profiles. Short lived excitonic states which are too broad to be resolved in linear spectroscopy are revealed by cross peaks in the photon-echo nonlinear technique. Signatures of the dynamic gap in the two-dimensional spectra are discussed. The effect of the Coulomb induced exciton-exciton scattering and the formation of biexciton molecules are demonstrated. 
O. Roslyak, G. Gumbs, S. Mukamel
cond-mat.mtrl-sci cond-mat.mes-hall