Downward shift of infrared conductivity spectral weight at the DDW transition: role of anisotropy

TL;DR

This paper investigates how the spectral weight in infrared conductivity shifts at the DDW transition, showing that anisotropy in quasiparticle lifetime explains the downward shift observed in experiments, supporting the DDW theory of the pseudogap.

Contribution

It demonstrates that anisotropic quasiparticle lifetime accounts for the downward spectral weight shift at the DDW transition, aligning theory with experimental observations.

Findings

Spectral weight shifts to higher frequencies with isotropic lifetime.

Spectral weight shifts to lower frequencies with anisotropic lifetime.

Supports DDW theory as explanation for pseudogap phenomena.

Abstract

We consider the motion of conductivity spectral weight at a finite-temperature phase transition at which $d_{x^2-y^2}$ density-wave (DDW) order develops. We show that there is a shift of spectral weight to higher frequencies if the quasiparticle lifetime is assumed to be isotropic, but a shift to lower frequencies if the quasiparticle lifetime is assumed to be anisotropic. We suggest that this is consistent with recent experiments on the pseudogap phase of the cuprate superconductors and, therefore, conclude that the observation of a downward shift in the spectral weight at the pseudogap temperature does not militate against the DDW theory of the pseudogap.