45 research outputs found

### 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

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

In the present work the multiband p-d model for $CuO_2$-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-$T_c$ compound.Comment: Submitted to ICM 2003 Conference 3 pages, 2 figure

### 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-$T_c$ 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