Infrared Conductivity and Charge Ordering in NaCoO2

Abstract

The infrared conductivity of NaxCoO2 is studied as a function of doping and temperature for x between 0.5 and 1. Charge localization in CoO2 layers shows up through a far-infrared peak (FIP) in the infrared conductivity which coexists with a small Drude contribution. Long-range ordering at x = 0.5 is confirmed to create a far-infrared gap, in addition to the FIP. At high x, the formation of a Spin-Density Wave reported below 22 K dramatically shifts the FIP to higher energy when x is incommensurate with the lattice, indicating an abrupt deepening of the localizing potential. The in-plane E1u phonon lifetime is shown to be sensitive to both "freezing" and ordering of the mobile Na+ ions. A comparison with the behavior of the FIP shows that such "freezing" is not the only origin of charge localization in the CoO layers.

7 pages, 4 figures

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Cited by in corpus (9)

• Angle-resolved photoemission study of cobalt oxide superconductor NaxCoO2.yH2O : Observation of the Fermi surface
• The infrared conductivity of Na${}_x$CoO${}_2$: evidence of gapped states
• Charge and Spin Ordering in Insulating Na${}_{0.5}$CoO${}_2$: Effects of Correlation and Symmetry
• Superconductivity in epitaxial thin films of NaxCoO2 y D2O
• Crystal-to-stripe reordering of sodium ions in NaxCoO2 (x>=0.75)
• Interplay of frustration, magnetism, charge ordering, and covalency in a model of Na0.5CoO2
• Chemical Differences between K and Na in Alkali Cobaltates
• Ionic Hubbard model on a triangular lattice for Na_0.5CoO_2, Rb_0.5CoO_2 and K_0.5CoO_2: Mean-field slave boson theory
• Electronic and magnetic properties of the ionic Hubbard model on the striped triangular lattice at 3/4 filling