ZERO TEMPERATURE PHASE-DIAGRAM OF A SMALL METALLIC JUNCTION

We discuss the phase diagram for a metal tunnel junction with quasiparticle dissipation. We present some evidences of a T = 0 phase transition induced by dissipation, by means of Monte Carlo simulation and studying the problem by means of a selfconsistent harmonic approximation. When the nominal conductance of the junction is large the predictions of the spin wave theory turn out to be correct and the algebraic decay of correlations implies quasi-long range order (phase with infinite susceptibility), this situation corresponds to the absence of a Coulomb blockade voltage threshold. The critical value of the nominal junction resistance is estimated to be R(t) almost-equal-to 0.6 k-OMEGA.