Transition from overscreening to underscreening in the multichannel Kondo model: exact solution at large N

TL;DR

This paper introduces a new large-N approach to the multichannel Kondo model using Schwinger bosons, revealing different screening regimes and preserving Fermi-liquid behavior in the exactly screened case.

Contribution

It presents an exact large-N solution for the multichannel Kondo model with Schwinger bosons, identifying regimes of underscreening, overscreening, and exact screening.

Findings

Identifies three distinct screening regimes in the model.

Derives saddle-point equations similar to the non-crossing approximation.

Calculates physical quantities analytically and numerically, confirming Fermi-liquid behavior in the exactly screened case.

Abstract

A novel large-N limit of the multichannel Kondo model is introduced, for representations of the impurity spin described by Schwinger bosons. Three cases are found, associated with underscreening, overscreening and exact Kondo screening of the impurity. The saddle-point equations derived in this limit are reminiscent of the ``non-crossing approximation'', but preserve the Fermi-liquid nature of the model in the exactly screened case. Several physical quantities are computed, both numerically, and analytically in the low-\omega,T limit, and compared to other approaches.