  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.
