We perturb about an exactly solvable point for the nonequilibrium Kondo problem. In each of the three independent directions in parameter space, the differential conductance evolves smoothly as one goes away from the solvable point, and the lowest-order correction contains the logarithm of the band width, or cutoff. Perturbing towards physically realistic exchange couplings yields differential-conductance curves which more closely resemble experimental data than at the solvable point. The leading coefficient which describes the low-temperature and low-voltage scaling changes as one perturbs away from the solvable point, indicating nonuniversal behavior; however, it is restored to the solvable-point value in the limit of an infinite band width.

• Received 31 July 1997

DOI:https://doi.org/10.1103/PhysRevB.57.2991