Holographic Kondo and Fano Resonances

TL;DR

This paper uses holography to analyze a strongly coupled 1+1D conformal field theory with an impurity, revealing how Kondo and Fano resonances manifest and persist across temperatures through RG flows.

Contribution

It demonstrates the holographic realization of Kondo and Fano resonances in a strongly correlated 1+1D CFT, highlighting a new mechanism for Fano resonance generation via RG flows.

Findings

Kondo resonance persists at all temperatures in spectral functions.

Fano resonances appear at all temperatures, linked to impurity spectral features.

Kondo effect occurs below a critical temperature in the large-N limit.

Abstract

We use holography to study a $(1+1)$-dimensional Conformal Field Theory (CFT) coupled to an impurity. The CFT is an $SU(N)$ gauge theory at large $N$, with strong gauge interactions. The impurity is an $SU(N)$ spin. We trigger an impurity Renormalization Group (RG) flow via a Kondo coupling. The Kondo effect occurs only below the critical temperature of a large-$N$ mean-field transition. We show that at all temperatures $T$, impurity spectral functions exhibit a Fano resonance, which in the low-$T$ phase is a large-$N$ manifestation of the Kondo resonance. We thus provide an example in which the Kondo resonance survives strong correlations, and uncover a novel mechanism for generating Fano resonances, via RG flows between $(0 + 1)$-dimensional fixed points