Conductivity activation energy for bilayer hetero-structures at integer   filling numbers
  We report on study of low-energy excitations in a bilayer hetero-structure 2D electron gas. We split the bilayer Hamiltonian into SU(4)-symmetric part and the anisotropy part and treat the latter as a perturbation. We find that both Goldstone and the charged excitations - skyrmions - are goverened by the non-linear Sigma Model. We calculate the anisotropic energy gap of the skyrmion to have a prominent minimum in the canted antiferromagnetic phase of bilayer. We compare our findings with the results of recent experiments. 
V.Falko (1), S.V.Iordanski (2) and A.Kashuba (2) ((1) Lancaster   University UK, (2) Landau Institute Moscow)