Effective Hamiltonian for transition-metal compounds: Application to NaxCoO2

Article

关键词: T-J MODEL;    HIGH-TEMPERATURE SUPERCONDUCTORS;    GENERALIZED HUBBARD-MODEL;    HOLE-DOPED Y2BANIO5;    CUPRATE SUPERCONDUCTORS;    CUO2 PLANES;    BAND-MODEL;    OXIDES;    DERIVATION;    PHOTOEMISSION;   

DOI  :  10.1103/PhysRevB.81.195113

来源: SCIE

【 摘 要 】

We describe a simple scheme to construct a low-energy effective Hamiltonian H-eff for highly correlated systems containing nonmetals such as O, P, or As (O in what follows) and a transition-metal (M) as the active part in the electronic structure, eliminating the O degrees of freedom from a starting Hamiltonian that contains all M d orbitals and all nonmetal p orbitals. We calculate all interaction terms between d electrons originating from Coulomb repulsion, as a function of three parameters (F-0, F-2, and F-4) and write them in a basis of orbitals appropriate for cubic, tetragonal, tetrahedral, or hexagonal symmetry around M. The approach is based on solving exactly (numerically if necessary) a MOn cluster containing the transition-metal atom and its n nearest O atoms (for example, a CoO6 cluster in the case of the cobaltates, or a CuOn cluster in the case of the cuprates, in which n depends on the number of apical O atoms), and mapping them into many-body states of the same symmetry containing d holes only. We illustrate the procedure for the case of NaxCoO2. The resulting H-eff, including a trigonal distortion D, has been studied recently and its electronic structure agrees well with angle-resolved photoemission spectra [A. Bourgeois, A. A. Aligia, and M. J. Rozenberg, Phys. Rev. Lett. 102, 066402 (2009)]. Although H-eff contains only 3d t(2g) holes, the highly correlated states that they represent contain an important amount not only of O 2p holes but also of 3d e(g) holes. When more holes are added, a significant redistribution of charge takes place. As a consequence of these facts, the resulting values of the effective interactions between t(2g) states are smaller than previously assumed, rendering more important the effect of D in obtaining only one sheet around the center of the Brillouin zone for the Fermi surface (without additional pockets)

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