Optical conductivity of unconventional charge density wave systems: Role of vertex corrections

TL;DR

This paper investigates how vertex corrections influence the optical conductivity in a d-charge density wave system, revealing their role in conductivity enhancement, spectral features, and sum rule violations across temperature and hopping parameters.

Contribution

It introduces a lowest-order conserving approximation to analyze vertex corrections' effects on optical conductivity in a d-CDW system, highlighting their impact on spectral properties and sum rule violations.

Findings

Vertex corrections enhance d.c. conductivity.

They narrow the Drude peak and alter spectral features.

Vertex corrections lead to a violation of the optical sum rule.

Abstract

The optical conductivity of a d-CDW conductor is calculated for electrons on a square lattice and a nearest-neighbor charge-charge interaction using the lowest-order conserving approximation. The spectral properties of the Drude-like peak at low frequencies and the broad hump due to transitions across the gap at large frequencies are discussed, also as a function of temperature and of the second-nearest neighbor hopping term t'. We find that vertex corrections enhance the d.c. conductivity, make the Drude peak narrower and provide a smooth transition from a renormalized regime at low to the bare theory at high frequencies. It is also shown that vertex corrections enhance the temperature dependence of the restricted optical sum leading to a non-negligible violation of the sum rule in the d-CDW state.