Development of the tunnelling gap in disordered 2D electron system with   magnetic field: observation of the soft-hard gap transition
  Magnetic field suppression of the tunneling between disordered 2D electron systems in GaAs around zero bias voltage has been studied. Magnetic field B normal to the layers induces a dip in the tunneling density of states (TDOS) centered precisely at the Fermi level, i.e. soft tunneling gap. The soft gap has a linear form with finite TDOS diminishing with B at the Fermi level. Driven by magnetic field the transition soft-hard gap has been observed, i.e. the TDOS vanishes in the finite energy window around Fermi level at B>13 T. 
Yu.V. Dubrovskii, V.A. Volkov, L. Eaves, E.E. Vdovin, O.N.   Makarovskii, J.-C. Portal, M. Henini and G. Hill