Hybridization of electron subbands in a double quantum well at   quantizing magnetic field
  We employ magnetocapacitance and far-infrared spectroscopy techniques to study the spectrum of the double-layer electron system in a parabolic quantum well with a narrow tunnel barrier in the centre. For gate-bias-controlled asymmetric electron density distributions in this soft two-subband system we observe both individual subband gaps and double layer gaps at integer filling factor $\nu$. The bilayer gaps are shown to be either trivial common for two subbands or caused by hybridization of electron subbands in magnetic field. We describe the observed hybrid gaps at $\nu=1$ and $\nu=2$ within a simple model for the modified bilayer spectrum. 
V.T.Dolgopolov, A.A.Shashkin, E.V.Deviatov, F.Hastreiter, M.Hartung,   A.Wixforth, K.L.Campman, A.C.Gossard