Non-Fermi-liquid fixed point in multi-orbital Kondo impurity model relevant for Hund's metals

TL;DR

This paper investigates a three-orbital Kondo impurity model relevant for Hund's metals, revealing a non-Fermi-liquid fixed point characterized by overscreening and distinct spin and orbital screening scales.

Contribution

It identifies a non-Fermi-liquid SU(3) fixed point in a simplified impurity model, elucidating intermediate state behavior in Hund's metals.

Findings

Discovery of a non-Fermi-liquid two-channel overscreened SU(3) fixed point.

Characterization of spin and orbital susceptibilities and their temperature dependence.

Identification of spectral function features indicative of the fixed point.

Abstract

Due to the separation between the spin and the orbital screening scales, the normal state of Hund's metals at ambient temperature can be loosely characterized as a partially coherent state with fluctuating spins and quenched orbital moments. With the aim to characterize this situation more precisely, we investigate the Kondo-Kanamori impurity model that describes the low-energy local physics of three-orbital Hund's metals occupied by two or four electrons. Within this model one can diminish the mixed spin-orbital terms and thereby enhance the separation between the two screening scales, allowing a more precise investigation of the intermediate state. Using the numerical renormalization group we calculate the impurity entropy as well as the temperature and frequency dependence of the spin and the orbital susceptibilities. We uncover a non-Fermi-liquid two-channel overscreened SU(3) fixed point that controls the behavior in the intermediate regime. We discuss its fingerprints in the frequency dependence of local orbital susceptibility and the shape of the spectral function.