Conductance of a spin-1 quantum dot: the two-stage Kondo effect

TL;DR

This paper models the conductance behavior of a spin-1 quantum dot exhibiting a two-stage Kondo effect, revealing a crossover from underscreened to fully screened regimes and the resulting conductance suppression at low temperatures.

Contribution

It introduces a large-N Schwinger boson-based model to describe the temperature-dependent conductance in a two-channel Kondo system with asymmetric couplings.

Findings

Identification of a broad crossover dominated by underscreened Kondo physics

Development of a model explaining conductance growth and suppression

Prediction of non-Fermi liquid corrections in the conductance

Abstract

We discuss the physics of a of a spin-1 quantum dot, coupled to two metallic leads and develop a simple model for the temperature dependence of its conductance. Such quantum dots are described by a two-channel Kondo model with asymmetric coupling constants and the spin screening of the dot by the leads is expected to proceed via a two-stage process. When the Kondo temperatures of each channel are widely separated, on cooling, the dot passes through a broad cross-over regime dominated by underscreened Kondo physics. A singular, or non-fermi liquid correction to the conductance develops in this regime. At the lowest temperatures, destructive interference between resonant scattering in both channels leads to the eventual suppression of the conductance of the dot. We develop a model to describe the growth, and ultimate suppression of the conductance in the two channel Kondo model as it is screened successively by its two channels. Our model is based upon large-N approximation in which the localized spin degrees of freedom are described using the Schwinger boson formalism.