Topological defects in the edge state structure in a bilayer electron   system
  We experimentally demonstrate, for the first time, formation of point-like topological defects in the edge state structure in the quantum Hall effect regime. By using of a selective population technique, we investigate equilibration processes between the edge states in bilayer electron structures with a high tunnelling rate between layers. Unexpected flattening of the I-V curves in perpendicular magnetic field at a specific filling factor combination and the recovery of the conventional nonlinear I-V characteristics in tilted fields give a strong evidence for the existence of topological defects. 
E.V. Deviatov, V.T. Dolgopolov, A. Wurtz, A. Lorke, A. Wixforth, W.   Wegscheider, K.L. Campman, A.C. Gossard