Optical response of high-$T_c$ cuprates: possible role of scattering rate saturation and in-plane anisotropy

TL;DR

This paper uses a generalized Drude model to analyze the in-plane optical conductivity of cuprates, emphasizing the importance of anisotropy and scattering rate saturation in understanding their electronic properties.

Contribution

It introduces a simple anisotropic scattering rate model with saturation effects that better fits experimental data and challenges previous assumptions of linear frequency dependence.

Findings

Anisotropy significantly affects optical conductivity analysis.

Scattering rate saturates at the Mott-Ioffe-Regel limit.

Previous models neglecting anisotropy may be incomplete.

Abstract

We present a generalized Drude analysis of the in-plane optical conductivity $\sigma_{ab}$($T$,$\omega$) in cuprates taking into account the effects of in-plane anisotropy. A simple ansatz for the scattering rate $\Gamma$($T$,$\omega$), that includes anisotropy, a quadratic frequency dependence and saturation at the Mott-Ioffe-Regel limit, is able to reproduce recent normal state data on an optimally doped cuprate over a wide frequency range. We highlight the potential importance of including anisotropy in the full expression for $\sigma_{ab}$($T$,$\omega$) and challenge previous determinations of $\Gamma$($\omega$) in which anisotropy was neglected and $\Gamma$($\omega$) was indicated to be strictly linear in frequency over a wide frequency range. Possible implications of our findings for understanding thermodynamic properties and self-energy effects in high-$T_c$ cuprates will also be discussed.