The 2-channel Kondo model II. CFT calculation of non-equilibrium conductance through a nanoconstriction containing 2-channel Kondo impurities

Recent experiments by Ralph and Buhrman on zero-bias anomalies in quenched Cu nanoconstrictions (reviewed in a preceding paper) are in accord with the assumption that the interaction between electrons and nearly degenerate two-level systems in the constriction can be described, for sufficiently small voltages and temperatures ( V, T < T-K), by the 2-channel Kondo (2CK) model. Motivated by these experiments, we introduce a generalization of the 2CK model, which we call the nanoconstriction 2-channel Kondo model (NTKM), that takes into account the complications arising From the non-equilibrium electron distribution in the nanoconstriction. We calculate the conductance G(V, T) of the constriction in the weakly non-equilibrium regime of V, T << T-K by combining concepts from Hershfieid's Y-operator formulation of non-equilibrium problems and Affleck and Ludwig's exact conformal field theory (CFT) solution of the 2CK problem (CFT technicalities will be discussed in a subsequent paper). Finally, we extract from the conductance a universal scaling curve Gamma(v) and compare it with experiment. Combining our results with those of Hettler, Kroha, and Hershfield, we conclude that the NTKM achieves quantitative agreement with the experimental scaling data. (C) 1999 Academic Press.