45 research outputs found

    Coupling angle resolved photoemission data and quasiparticle structure in antiferromagnetic insulators Sr2CuO2Cl2 and Ca2CuO2Cl2

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    We have analyzed the quasiparticle dispersion and ARPES-spectral density for Sr2CuO2Cl2 and Ca2CuO2Cl2 antiferromagnetic insulators along basic symmetric directions of the Brillouin zone (BZ) in a framework of an extended tight binding method (ETBM) with explicit account for intracell strong electron correlations. The quasiparticle dispersion is in a good agreement with ARPES- data. At the top of valence band we found a narrow impurity-like virtual level with the spectral weight proportional to the concentration of spin fluctuations. A pseudogap between the virtual level and the top of the valence band has dispersion similar to 'remnant Fermi surface' in Ca2CuO2Cl2 and to a pseudogap in the underdoped Bi2212 samples. A calculated parity of the polarized ARPES-spectra in (0,0),(pi/2,pi/2),(pi,0) - points in the AFM- phase is even with regard to relative magnitudes of the partial contributions by different orbitals to the total ARPES- spectral density. Conditions of an observability for the different partial contributions in the polarized ARPES- experiments are determined also.Comment: 15 pdf-pages with 10 figures and tabl

    Spin fluctuations influence on quasiparticle spectrum of realistic p-d model

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    In the present work the multiband p-d model for CuO2CuO_2-layer is treated. It was shown that for the realistic set of parameters besides Zhang-Rice two-particle singlet there is non-negligible contribution of two-particle triplet state to the top of the valence band. Also shown, that to gain quantitative agreement with experimental data the minimal approximation should include the spin fluctuations beyond the Hubbard-I scheme. Quasiparticle spectrum, obtained in this approximation, is in fairly good agreement with ARPES data on Bi2212 High-TcT_c compound.Comment: Submitted to ICM 2003 Conference 3 pages, 2 figure

    The t-J model on a semi-infinite lattice

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    The hole spectral function of the t-J model on a two-dimensional semi-infinite lattice is calculated using the spin-wave and noncrossing approximations. In the case of small hole concentration and strong correlations, tJt\gg J, several near-boundary site rows appear to be depleted of holes. The reason for this depletion is a deformation of the magnon cloud, which surrounds the hole, near the boundary. The hole depletion in the boundary region leads to a more complicated spectral function in the boundary row in comparison with its bulk shape.Comment: 8 pages, 5 figure

    Strong spin triplet contribution of the first removal state in the insulating regime of Bi2Sr2Ca1-xYxCu2O8+delta

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    The experimental dispersion of the first removal state in the insulating regime of Bi2Sr2Ca1-xYxCu2O8+delta is found to differ significantly from that of other parent materials: oxyclorides and La2CuO4 . For Y-contents of 0.92 > x > 0.55 due to nonstoichiometric effects in the Bi-O layers, the hole concentration in the CuO2 -layers is almost constant and on the contrary the crystal lattice parameters a,b,c change very strongly. This (a,b) parameter increase and c parameter decrease results in an unconventional three peak structure at (0,0);(pi/2, pi/2);(pi,pi) for x=0.92. We can describe the experimental data only beyond the framework of the 3-band pd-model involving the representations of a new triplet counterpart for the Zhang-Rice singlet state.Comment: 16 pages, 4 figure

    Parameters of the Effective Singlet-Triplet Model for Band Structure of High-TcT_c Cuprates by Different Approaches

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    The present paper covers the problem of parameters determination for High-TcT_c superconductive copper oxides. Different approaches, {\it ab initio} LDA and LDA+U calculations and Generalized Tight-Binding (GTB) method for strongly correlated electron systems, are used to calculate hopping and exchange parameters of the effective singlet-triplet model for CuO2CuO_2-layer. The resulting parameters are in remarkably good agreement with each other and with parameters extracted from experiment. This set of parameters is proposed for proper quantitative description of physics of hole doped High-TcT_c cuprates in the framework of effective models.Comment: PACS 74.72.h; 74.20.z; 74.25.Jb; 31.15.A