Eur. Phys. J. B 40, 231-234 (2004)
https://doi.org/10.1140/epjb/e2004-00275-9

Optical evidence for the proximity to a spin-density-wave metallic state in Na_0.7CoO₂

¹ Laboratorium für Festkörperphysik, ETH Zürich, 8093 Zürich, Switzerland
² Institut de physique de la matière complexe (IPMC), EPF Lausanne, 1015 Lausanne, Switzerland
³ Institute of Mineralogy and Geochemistry, University of Lausanne, 1015 Lausanne, Switzerland

Corresponding author: ^a degiorgi@solid.phys.ethz.ch

Received: 16 May 2004
Revised: 6 August 2004
Published online: 9 September 2004

Abstract

We present the optical properties of Na_0.7CoO₂ single crystals, measured over a broad spectral range as a function of temperature (T). The capability to cover the energy range from the far-infrared up to the ultraviolet allows us to perform reliable Kramers-Kronig transformation, in order to obtain the absorption spectrum (i.e., the complex optical conductivity). To the complex optical conductivity we apply the generalized Drude model, extracting the frequency dependence of the scattering rate (Γ) and effective mass (m^*) of the itinerant charge carriers. We find that at low temperatures and for . This suggests that Na_0.7CoO₂ is at the verge of a spin-density-wave metallic phase.