  Non-Ohmic tunnel junctions are believed to occur in systems where the exciton
and orthogonality catastrophe effects significantly modify tunneling rates.
Here we present a simple non-perturbative treatment of the thermodynamic and
transport properties of subOhmic and superOhmic tunnel junctions. The large-N
approximation demonstrates the existence of a quantum phase transition in
subOhmic but not superOhmic tunnel junctions. In addition, we find a pseudogap
which vanishes continuously as the transition is approached.
