Interorbital Charge Transfers and Fermi-Surface Deformations in Strongly Correlated Metals : Models, BaVS_3 and Na_xCoO_2(Yukawa International Seminar 2004 (YKIS2004) Physics of Strongly Correlated Electron Systems)

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Fermi-surface deformations in strongly correlated metals, in comparison to results from band-structure calculations, are investigated. We show that correlation-induced interband charge transfers in multi-orbital systems may give rise to substantial modifications of the actual Fermi surface. Depending in particular on the relative strength of the crystal-field splitting and of the Hund's exchange coupling, correlations may either reinforce orbital polarization or tend to compensate differences in orbital occupancies, as demonstrated by investigating a 2-band Hubbard model in the framework of dynamical mean field theory (DMFT). The physical implications of such interorbital charge transfers are then explored in two case studies : BaVS_3 and Na_xCoO_2. By means of the DMFT in combination with the local density approximation (LDA) to density functional theory (DFT), new insights in the underlying mechanism of the metal-to-insulator transition (MIT) of BaVS_3 are obtained. A strong charge redistribution in comparison to LDA calculations, i.e., a depletion of the broader A_<1g> band in favor of the narrower E_g bands just above the MIT is found. In addition, the intriguing problem of determining the Fermi surface in the strongly correlated cobaltate system Na_xCoO_2 is discussed.
理論物理学刊行会の論文
2006-02-06