A new non-Fermi liquid fixed point

TL;DR

This paper introduces a novel non-Fermi liquid fixed point arising from an overscreened exchange interaction between conduction electrons with pseudo spin 3/2 and an impurity spin 1/2, analyzed through NRG and conformal field theory.

Contribution

It identifies a new non-Fermi liquid fixed point with unique spectral and thermodynamic properties, expanding understanding of overscreened Kondo systems.

Findings

Low-energy spectra exhibit non-Fermi liquid behavior.

Specific heat and susceptibility diverge as T^{-2/3}.

Magnetic field scaling dimension is 5/6.

Abstract

We study a new exchange interaction in which the conduction electrons with pseudo spin $S_c=3/2$ interact with the impurity spin $S_I=1/2$. Due to the overscreening of the impurity spin by higher conduction electron spin, a new non-trivial intermediate coupling strength fixed point is realized. Using the numerical renormalization group (NRG), we show that the low-energy spectra are described by a non-Fermi liquid excitation spectrum. A conformal field theory analysis is compared with NRG results and excellent agreement is obtained. Using the double fusion rule to generate the operator spectrum with the conformal theory, we find that the specific heat coefficient and magnetic susceptibility will diverge as $T^{-2/3}$, that the scaling dimension of an applied magnetic field is $5/6$, and that exchange anisotropy is always relevant. We discuss the possible relevance of our work to two-level system Kondo materials and dilute cerium alloys, and we point out a paradox in understanding the Bethe-Ansatz solutions to the multichannel Kondo model.