Construction of a multielectron basis for Mott insulators with strong electron correlations, spin-orbit interaction, and
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C PROPERTIES OF SOLID
Construction of a Multielectron Basis for Mott Insulators with Strong Electron Correlations, Spin–Orbit Interaction, and Covalence Yu. S. Orlova, * and S. G. Ovchinnikova,b, ** a
Kirenskiі Institute of Physics, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia *email: [email protected] **email: [email protected] b Siberian Federal University, Krasnoyarsk, 660041 Russia Received March 4, 2009
Abstract—We propose that the apparatus of quantum mechanics of a free atom (in particular, the theory of nj symbols and Rakah–Wigner genealogic coefficients generalized to the case of point groups and widely used in crystal field theory) be used for constructing multielectron bases with allowance for covalence and spin– orbit interaction. This allows us to take into account the electron–electron interaction for 3d ions the most comprehensively. The basis constructed in this way can be used in the generalized strong coupling method for the multiband p–d model in describing the structure of the quasiparticle energy spectrum and physical prop erties of systems with strong electron correlations. The procedure of construction and computation is dem onstrated for the 5T2g term in the d6 configuration of the transition metal atom in an octahedral field. The mechanism for the emergence of magnetic anisotropy in S ions (Fe3+ and Mn2+) due to covalent mixing of d6 L configurations with a nonzero orbital angular momentum ( L is a hole in ligands) is demonstrated. PACS numbers: 71.10.w, 71.15.m, 71.27.+a DOI: 10.1134/S1063776109080196
1. INTRODUCTION Electron correlations play an important role in the formation of various magnetic and transport proper ties of transition metal oxides. Many attempts have been made in recent years to describe these properties and primarily the metal–insulator transition, super conductivity in cuprates, and colossal magnetoresis tance in manganites. Mott [1, 2] and Hubbard [3] demonstrated that it is the strong Coulomb d–d inter action that explains the existence of many transition 3d metal oxide compounds with a partly filled 3d band in the form of magnetic insulators. A compound is a metal if the width of the 3d band is larger than the Coulomb d–d interaction. If, however, the Coulomb interaction exceeds the bandwidth, 3d electrons are localized, the compound becomes an insulator with localized magnetic moments, and the dielectric gap width is determined by the intensity of the electron– electron interaction. In other words, a strong (Cou lomb or exchange) interaction of 3d electrons exceed ing or on the order of their kinetic energy (with the electron bandwidth as a measure) renders these sub stances the properties of strongly correlated systems, which complicates theoretical description of their physical properties.
In [4], a scheme was proposed in which transition metal compounds can be classified in accordance with two regimes depending on the relation between ligandtometal charge transfer energy ∆tr and Cou lomb energy U. In the Mott–Hubbard
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