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Na$_x$CoO$_2$ in the x -> 0 Regime: Coupling of Structure and Correlation effects

K. -W. Lee·W. E. Pickett
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Abstract

The study of the strength of correlations in Na$_x$CoO$_2$ is extended to the x=0 end of the phase diagram where Mott insulating behavior has been widely anticipated. Inclusion of correlation as modeled by the LDA+U approach leads to a Mott transition in the $a_g$ subband if U is no less than U$_c$=2.5 eV. Thus U smaller than U$_c$ is required to model the metallic, nonmagnetic CoO$_2$ compound reported by Tarascon and coworkers. The orbital-selective Mott transition of the $a_g$ state, which is essentially degenerate with the $e'_{g}$ states, occurs because of the slightly wider bandwidth of the $a_g$ bands. The metal-insulator transition is found to be strongly coupled to the Co-O bond length, due to associated changes in the $t_{2g}$ bandwidth, but the largest effects occur only at a reduced oxygen height that lies below the equilibrium position.

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K. -W. Lee, W. E. Pickett. 2005-05-24. Na$_x$CoO$_2$ in the x -> 0 Regime: Coupling of Structure and Correlation effects. https://doi.org/10.1103/physrevb.72.115110

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