The infrared spectrum of Na_0.57CoO_2

TL;DR

This study investigates the optical conductivity of Na_0.57CoO_2, revealing strong electron-phonon interactions and a high effective mass, with implications for understanding its electronic properties and similarities to high-temperature cuprates.

Contribution

First report of the optical conductivity of Na_0.57CoO_2, highlighting strong electron-phonon coupling and its effects on carrier dynamics.

Findings

Carrier effective mass of 5 electron masses

Evidence of strong electron-phonon coupling via Fano distortion

Optical peak at 8800 cm^-1 scales with high-T_c cuprates' charge transfer band

Abstract

The optical conductivity of single crystals of Na_xCoO_2 for $x$ = 0.57 is first reported between 295 and 30 K. In the far infrared, an "anomalous Drude" analysis leads to a carrier effective mass of 5 electron masses. That this high value is due to strong electron-phonon coupling is suggested by the Fano distortion of a phonon at 570 cm^-1. A peak at 8800 cm^-1 scales with the charge transfer band of several high-$T_c$ cuprates by simply replacing the in-plane Cu-O bond length with that for Co-O.