Universal low-temperature crossover in two-channel Kondo models

TL;DR

This paper derives an exact Green function for two-channel Kondo models, revealing a universal crossover from non-Fermi liquid to Fermi liquid behavior, with implications for quantum dot conductance and experimental observations.

Contribution

It provides the first exact expression for the electron Green function capturing the full crossover in two-channel Kondo models, connecting NFL and FL regimes.

Findings

Universal Green function describing crossover behavior

Agreement with numerical renormalization group results

Distinct conductance signatures in quantum dot experiments

Abstract

An exact expression is derived for the electron Green function in two-channel Kondo models with one and two impurities, describing the crossover from non-Fermi liquid (NFL) behavior at intermediate temperatures to standard Fermi liquid (FL) physics at low temperatures. Symmetry-breaking perturbations generically present in experiment ensure the standard low-energy FL description, but the full crossover is wholly characteristic of the unstable NFL state. Distinctive conductance lineshapes in quantum dot devices should result. We exploit a connection between this crossover and one occurring in a classical boundary Ising model to calculate real-space electron densities at finite temperature. The single universal finite-temperature Green function is then extracted by inverting the integral transformation relating these Friedel oscillations to the t matrix. Excellent agreement is demonstrated between exact results and full numerical renormalization group calculations.