Transport anomalies in a simplified model for a heavy electron quantum critical point

TL;DR

This paper models transport anomalies at a heavy electron quantum critical point, revealing a sudden charge acquisition by spin excitations and a linear growth of Drude weight, indicating a gossamer Fermi-liquid phase.

Contribution

It introduces a large-N treatment of the Kondo-Heisenberg lattice model showing how charge emerges in spin excitations and characterizes the transport properties at the quantum critical point.

Findings

Both linear and Hall conductivity jump at the transition.

Drude weight grows linearly with distance from the critical point.

Heavy fermion phase behaves like a Meissner phase with a gossamer Fermi-liquid.

Abstract

We discuss the transport anomalies associated with the development of heavy electrons out of a neutral spin fluid using the large-N treatment of the Kondo-Heisenberg lattice model. At the phase transition in this model the spin excitations suddenly acquire charge. The Higgs process by which this takes place causes the constraint gauge field to loosely ``lock'' together with the external, electromagnetic gauge field. From this perspective, the heavy fermion phase is a Meissner phase in which the field representing the difference between the electromagnetic and constraint gauge field, is excluded from the material. We show that at the transition into the heavy fermion phase, both the linear and the Hall conductivity jump together. However, the Drude weight of the heavy electron fluid does not jump at the quantum critical point, but instead grows linearly with the distance from the quantum critical point, forming a kind of ``gossamer'' Fermi-liquid.