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Nax_xCoO2_2 in the x -> 0 Regime: Coupling of Structure and Correlation effects

Abstract

The study of the strength of correlations in Nax_xCoO2_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 aga_g subband if U is no less than Uc_c=2.5 eV. Thus U smaller than Uc_c is required to model the metallic, nonmagnetic CoO2_2 compound reported by Tarascon and coworkers. The orbital-selective Mott transition of the aga_g state, which is essentially degenerate with the egβ€²e'_{g} states, occurs because of the slightly wider bandwidth of the aga_g bands. The metal-insulator transition is found to be strongly coupled to the Co-O bond length, due to associated changes in the t2gt_{2g} bandwidth, but the largest effects occur only at a reduced oxygen height that lies below the equilibrium position.Comment: 8 pages with 9 embedded figure

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    Last time updated on 02/01/2020