Signature of Kondo breakdown quantum criticality in optical conductivity

TL;DR

This paper investigates the optical conductivity near a Kondo breakdown quantum critical point in heavy fermion systems, revealing unique signatures such as a shifting inter-band transition peak that signals electron decoupling.

Contribution

It identifies distinctive optical conductivity features as signatures of Kondo breakdown quantum criticality, providing a way to distinguish it from other phase transitions.

Findings

Peak position shifts to lower energies but remains finite at the critical point

Peak value changes non-monotonically and disappears at the quantum critical point

Signatures can help experimentally identify Kondo breakdown transition

Abstract

We study the finite-frequency inter-band transition peak in the optical conductivity of a heavy fermion system close to a Kondo breakdown quantum critical point, where the lattice Kondo temperature vanishes. As the system approaches the phase transition from the heavy Fermi liquid side, we find a new cross-over regime where the peak position is related to, but is not directly proportional to, the lattice Kondo scale. In particular, the position of the peak moves to lower energies, but remains finite at the critical point. On the other hand, the peak value changes non-monotonically and eventually the peak disappears at the quantum critical point, indicating the decoupling of the narrow band of f-electrons from the conduction band. We argue that these are unique signatures of a Kondo breakdown transition, and therefore can be useful to distinguish it experimentally from a spin density wave instability.