Quantum Boltzmann equation study for the Kondo breakdown quantum criticalpoint

Abstract

We develop the quantum Boltzmann equation approach for the Kondo breakdown quantumcritical point, involved with two bands for conduction electrons and localized fermions.Particularly, the role of vertex corrections in transport is addressed, crucial fornon-Fermi liquid transport with temperature linear dependence. Only one bandof spinons may be considered for scattering with gauge fluctuations, and theirassociated vertex corrections are introduced in the usual way, where the divergence ofself-energy corrections is cancelled by that of vertex corrections, giving rise to aphysically meaningful result in the gauge invariant expression for conductivity.On the other hand, two bands should be taken into account for scattering withhybridization excitations, giving rise to coupled quantum Boltzmann equations. We findthat vertex corrections associated with hybridization fluctuations turn out to beirrelevant due to the heavy mass of spinons in the so called decoupling limit,consistent with the diagrammatic approach showing non-Fermi liquid transport.