Opening an energy gap in an electron double layer system at integer   filling factor in a tilted magnetic field
  We employ magnetocapacitance measurements to study the spectrum of a double layer system with gate-voltage-tuned electron density distributions in tilted magnetic fields. For the dissipative state in normal magnetic fields at filling factor $\nu=3$ and 4, a parallel magnetic field component is found to give rise to opening a gap at the Fermi level. We account for the effect in terms of parallel-field-caused orthogonality breaking of the Landau wave functions with different quantum numbers for two subbands. 
E.V. Deviatov, V.S. Khrapai, A.A. Shashkin, V.T. Dolgopolov (Institute   of Solid State Physics RAS, Chernogolovka, Russia) ...