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

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

The t-J model on a semi-infinite lattice

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, $t\gg J$, 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

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

The present paper covers the problem of parameters determination for High-$T_c$ 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 $CuO_2$-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-$T_c$ cuprates in the framework of effective models.Comment: PACS 74.72.h; 74.20.z; 74.25.Jb; 31.15.A

The Fermi surface and the role of electronic correlations in Sm2−x_{2-x}Cex_{x}CuO4_4

Using LDA+GTB (local density approximation+generalized tight-binding) hybrid scheme we investigate the band structure of the electron-doped high-$T_c$ material Sm$_{2-x}$Ce$_{x}$CuO$_4$. Parameters of the minimal tight-binding model for this system (the so-called 3-band Emery model) were obtained within the NMTO ($N$-th order Muffin-Tin orbital) method. Doping evolution of the dispersion and Fermi surface in the presence of electronic correlations was investigated in two regimes of magnetic order: short-range (spin-liquid) and long-range (antiferromagnetic metal). Each regime is characterized by the specific topologies of the Fermi surfaces and we discuss their relation to recent experimental data.Comment: 10 pages, 4 figures, 1 table, Published versio