arXiv subjects

A. L. Chernyshev

Publications and source records attributed to A. L. Chernyshev.

80 records · Page 5Linked to original sources

arXiv1996

Generalized $t$-$t^\prime$-$J$ model: parameters and single-particle spectrum for electrons and holes in copper oxides

A microscopically based Hamiltonian of the generalized $t$-$t^\prime$-$J$ model is presented. Two types of the additional $t^\prime$-terms are discussed. The set of ranges of the additional $t^\prime$-terms for the real CuO$_2$ planes is derived from the three-band model calculations. Using the variational spin-polaron approach the single-carrier dispersions in the generalized $t$-$t^\prime$-$J$ model are calculated both for the hole- and electron-doped systems. Hole and electron band minima are found to be at points $(0,\pmπ)$, $(\pmπ,0)$, and $(\pmπ/2,\pmπ/2)$, respectively. The band minima shifts $|Δ_{(0,π)-(π/2,π/2)}|$ are not small ($\sim J$). Bandwidths for both cases of doping are found to be $1.5-4.5$ times larger than the t-J model ones.

cond-mat↗

arXiv1995

Hole-hole superconducting pairing in the t-J model induced by spin-wave exchange

We study numerically the hole pairing induced by spin-wave exchange. The contact hole-hole interaction is taken into account as well. It is assumed that antiferromagnetic order is preserved at all scales relevant to pairing. The strongest pairing is obtained for the d-wave symmetry of the gap. Dependence of the value of the gap on hole concentration and temperature is presented. For the critical temperature we obtain Tc about 100 K at the hole concentration delta = 0.2-0.3.

cond-mat↗

arXiv1994

Range of the t--J model parameters for CuO$_{2}$ plane: experimental data constraints

The t-J model effective hopping integral is determined from the three-band Hubbard model for the charge carriers in CuO$_{2}$ plane. For this purpose the values of the superexchange constant $J$ and the charge-transfer gap $E_{gap}$ are calculated in the framework of the three-band model. Fitting values of $J$ and $E_{gap}$ to the experimental data allows to narrow the uncertainty region of the three-band model parameters. As a result, the $t/J$ ratio of the t-J model is fixed in the range $2.4 ÷2.7$ for holes and $2.5 ÷3.0$ for electrons. Formation of the Frenkel exciton is justified and the main features of the charge-transfer spectrum are correctly described in the framework of this approach.

cond-mat↗

arXiv1993

Hole-Hole Contact Interaction in the t-J Model

Using an analytical variational approach we calculate the hole-hole contact interaction on the Néel background. Solution of the Bethe-Salpeter equation with this interaction gives bound states in $d$- and p-waves with binding energies close to those obtained by numerical methods. At $t/J \ge 2-3$ the bound state disappears. In conclusion we discuss the relation between short range and long range interactions and analogy with the problem of pion condensation in nuclear matter.

cond-mat↗

arXiv1993

Consistent low-energy reduction of the three-band model for copper oxides with O-O hopping to the effective t-J model

A full three-band model for the CuO$_{2}$ plane with inclusion of all essential interactions - Cu-O and O-O hopping, repulsion at the copper and oxygen and between them - is considered. A general procedure of the low-energy reduction of the primary Hamiltonian to the Hamiltonian of the generalized $t$-$t'$-$J$ model is developed. An important role of the direct O-O hopping is discussed. Parameters of the effective low-energy model (the hopping integral, the band position and the superexchange constant $J$ are calculated. An analysis of the obtained data shows that the experimental value of $J$ fixes the charge transfer energy $Δ=(ε_{p}-ε_{d})$ in a narrow region of energies.

cond-mat↗

arXiv1993

The representations of the Hubbard algebra in terms of spin-fermion operators and motion of a hole in an antiferromagnetic state

The representation of the Hubbard operators in terms of the spin$-\frac{1}{2}$ operators and the fermion operator with spin$-\frac{1}{2}$ is proposed. In the low-energy limit this representation is reduced to the representation following from the Hubbard diagramm technique. In framework of this approach motion of a hole in an antiferromagnetic state of the t-J model is considered. It is shown that the primary hole energy is strongly renormalized and the band width has an order of J rather than t. The functional integral for the strongly correlated model induced by the obtained representation is formulated. The representation of the total Hubbard algebra for states in the lower and the upper Hubbard bands is formulated in terms of the spin$-\frac{1}{2}$ and two fermion fields with spin$-\frac{1}{2}$ is formulated.

cond-mat↗

arXiv1993

Low-energy limit of the three-band model for electrons in a CuO$_{2}$ plane

The three-band model with the O-O direct hopping near to unit filling is considered. We present the general procedure of reduction of this model to the low-energy limit. At unit filling the three-band model in the charge-transfer limit is reduced to the Heisenberg model and we calculate the superexchange constant. For the case of the small electron doping the three-band model is reduced to the $t-J$ model and we calculate electron hopping parameters at the nearest and next neighbors. We derive the structure of corrections to the $t-J$ model and calculate their magnitude. The values of the hopping parameters for electron- and hole-doping differ approximately at 40 %.

cond-mat↗

arXiv1993

Reduction of three-band model for copper oxides to single-band generalized t~-~J model

A three-band model for copper oxides in the region of parameters where the second hole on the copper has energy close to the first hole on the oxygen is considered. The exact solution for one hole on a ferromagnetic background of the ordered copper spins is obtained. A general procedure for transformation of the primary Hamiltonian to the Hamiltonian of singlet and triplet excitations is proposed. Reduction of the singlet-triplet Hamiltonian to the single-band Hamiltonian of the generalized t~-~J model is performed. A comparison of the solution for the generalized t~-~J model on a ferromagnetic background with the exact solution shows a very good agreement.

cond-mat↗