Stable two-channel Kondo fixed point of an SU(3) quantum defect in a metal: renormalization group analysis and conductance spikes

TL;DR

This paper presents a theoretical model for a two-channel Kondo effect in a metal with a quantum defect, explaining conductance spikes through renormalization group analysis and identifying a new low-energy scale.

Contribution

It introduces a physical realization of the 2CK effect with a three-state defect and demonstrates how a new low-energy scale explains conductance spikes.

Findings

Stabilization of the 2CK fixed point via electron interactions

Identification of a second low-energy scale below T_K

Explanation of conductance spikes in metallic point contacts

Abstract

We propose a physical realization of the two-channel Kondo (2CK) effect, where a dynamical defect in a metal has a unique ground state and twofold degenerate excited states. In a wide range of parameters the interactions with the electrons renormalize the excited double downward below the bare defect ground state, thus stabilizing the 2CK fixed point. In addition to the Kondo temperature T_K the three-state defect exhibits another low-energy scale, associated with ground-to-excited-state transitions, which can be exponentially smaller than T_K. Using the perturbative nonequilibrium renormalization group we demonstrate explicitly that this can provide the long-sought explanation of the sharp conductance spikes observed by Ralph and Buhrman in ultrasmall metallic point contacts.