Infrared Hall conductivity of Na$_{0.7}$CoO$_2$

TL;DR

This study investigates the infrared Hall conductivity of Na$_{0.7}$CoO$_2$ thin films, revealing two types of hole conduction with distinct behaviors and temperature dependencies, providing insights into the material's charge dynamics.

Contribution

It presents the first detailed analysis of infrared Hall conductivity in Na$_{0.7}$CoO$_2$, identifying coherent and incoherent carriers and their temperature-dependent spectral features.

Findings

Coherent Drude carriers exhibit large effective mass and Fermi liquid behavior.

Spectral weight of coherent carriers vanishes at 120K.

Infrared Hall constant remains positive and nearly temperature-independent.

Abstract

We report infrared Hall conductivity $\sigma_{xy}(\omega)$ of Na$_{0.7}$CoO$_2$ thin films determined from Faraday rotation angle $\theta_{F}$ measurements. $\sigma_{xy}(\omega)$ exhibits two types of hole conduction, Drude and incoherent carriers. The coherent Drude carrier shows a large renormalized mass and Fermi liquid-like behavior of Hall scattering rate, $\gamma_{H} \sim aT^{2}$. The spectral weight is suppressed and disappears at T = 120K. The incoherent carrier response is centered at mid-IR frequency and shifts to lower energy with increasing T. Infrared Hall constant is positive and almost independent of temperature in sharp contrast with the dc-Hall constant.