Na_xCoO₂ in the x -> 0 Regime: Coupling of Structure and Correlation effects

2005/05/24 by K. -W. Lee, W. E. Pickett
Physics and Astronomy · #cond-mat.str-el #cond-mat.supr-con

paper · pdf · doi:10.1103/physrevb.72.115110

published as Phys. Rev. B 72, 115110 (2005) · 8 pages with 9 embedded figures

arxiv created 2005/05/24 · arxiv updated 2009/12/01

Abstract

The study of the strength of correlations in Na_xCoO₂ 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 CoO₂ 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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