Multi-scale fluctuations near a Kondo Breakdown Quantum Critical Point

TL;DR

This paper investigates quantum criticality in the Kondo-Heisenberg model, revealing fluctuation behaviors near a Kondo breakdown point that explain experimental observations in heavy fermion metals.

Contribution

It introduces a fermionic mean-field analysis of the Kondo-Heisenberg model, identifying a quantum critical point with specific fluctuation dynamics and their experimental implications.

Findings

Critical fluctuations with dynamical exponent z=3 above 1 mK.

Logarithmic divergence of specific heat coefficient with temperature.

T log T behavior in resistivity consistent with experiments.

Abstract

We study the Kondo-Heisenberg model using a fermionic representation for the localized spins. The mean-field phase diagram exhibits a zero temperature quantum critical point separating a spin liquid phase where the f-conduction hybridization vanishes, and a Kondo phase where it does not. Two solutions can be stabilized in the Kondo phase, namely a uniform hybridization when the band masses of the conduction electrons and the f spinons have the same sign, and a modulated one when they have opposite sign. For the uniform case, we show that above a very small Fermi liquid temperature scale (~1 mK), the critical fluctuations associated with the vanishing hybridization have dynamical exponent z=3, giving rise to a specific heat coefficient that diverges logarithmically in temperature, as well as a conduction electron inverse lifetime that has a T log T behavior. Because the f spinons do not carry current, but act as an effective bath for the relaxation of the current carried by the conduction electrons, the latter result also gives rise to a T log T behavior in the resistivity. This behavior is consistent with observations in a number of heavy fermion metals.