LOCALIZED (POLARONIC) CHARGE-TRANSFER EXCITATIONS IN CuO2 LAYERS

1991 ◽  
Vol 05 (22) ◽  
pp. 1515-1523 ◽  
Author(s):  
J. LORENZANA ◽  
L. YU
Keyword(s):  
Charge Transfer ◽  
Degrees Of Freedom ◽  
High Temperature Superconductors ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Hartree Fock ◽  
The Mean ◽  
Transfer Origin ◽  
D Model ◽  
Definite Statement

We show that the recently found polarons and excitons of charge-transfer origin in the 1D p−d model of high temperature superconductors can also occur in 2D. We use a 2D spinless model which is expected to qualitatively describe the charge degrees of freedom of the p−d model in the limit of infinite on-site Coulomb repulsion on both Cu and O. The Cu-O repulsion Upd is treated by an unrestricted Hartree-Fock scheme. We found that in addition to polarons and excitons, other nonlinear excitations like bipolarons and clustering of carriers (phase separation) arise as well. Since the energies of all these excitations are very close to each other at the mean field level, no definite statement can be made about the true ground state.

Slave Boson Description of CuO2 Planes of the High-Temperature Superconductors

2003 ◽  
Vol 17 (18n20) ◽  
pp. 3277-3280 ◽  
Author(s):  
Ivana Mrkonjić ◽  
Slaven Barišić
Keyword(s):  
Charge Transfer ◽  
High Temperature ◽  
High Temperature Superconductors ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Field Calculation ◽  
Transfer Energy ◽  
Doping Dependence ◽  
Conducting State ◽  
Charge Transfer Energy

Slave-boson mean-field calculation is carried out analytically for doped CuO 2 conduction planes, described by the extended Emery model which is parameterized by Cu–O charge transfer energy Δpd, Cu–O hopping t0, O–O hopping t′ and Coulomb repulsion U localized on Cu site, taken as infinite. At zero doping δ, finite small t′ expands the range of stability of the covalent, conducting state, characterized by renormalized band parameters Δpf and t, on the expense of insulating t=0 state, which, however, remains stable at larger Δpd. For sufficiently large Δpd, Δpf saturates at 4|t′|. Finite doping suppresses the insulating state nearly symmetrically with respect to its sign. The regime with Δpf close to 4|t′| fits remarkably well ARPES spectra of Y123, Bi2212 and LSCO, and, in the latter case, explains the observed strong doping-dependence of the effective Cu–O hopping.

scholarly journals RELATIVE MOTION CORRECTION TO FISSION BARRIERS

2008 ◽  
Vol 17 (01) ◽  
pp. 151-159 ◽  
Author(s):  
J. SKALSKI
Keyword(s):  
Relative Motion ◽  
Cluster Model ◽  
Motion Correction ◽  
Mean Field Theory ◽  
Mean Field ◽  
Ternary Fission ◽  
Skyrme Interaction ◽  
Hartree Fock ◽  
Fission Barriers ◽  
The Mean

We discuss the effect of kinetic energy of the relative motion becoming spurious for separate fragments on the selfconsistent mean-field fission barriers. The treatment of the relative motion in the cluster model is contrasted with the necessity of a simpler and approximate approach in the mean-field theory. A scheme of the energy correction to the Hartree-Fock is proposed. The results obtained with the effective Skyrme interaction SLy 6 show that the correction, previously estimated as ~ 8 MeV in A = 70 - 100 nuclei, amounts to 4 MeV in the medium heavy nucleus 198 Hg and to null in 238 U . However, the corrected barrier implies a shorter fission half-life of the latter nucleus. The same effect is expected to lower barriers for multipartition (i.e. ternary fission, etc) and make hyperdeformed minima less stable.

NEUTRON–PROTON PAIRING CORRELATION FOR THE ROTATIONAL MOTION OF N = Z72Kr, 76Sr, AND 80Zr NUCLEI

2011 ◽  
Vol 20 (08) ◽  
pp. 1687-1699
Author(s):  
PRIANKA ROY ◽  
SHASHI K. DHIMAN
Keyword(s):  
Effective Interaction ◽  
Mean Field ◽  
High Spin State ◽  
Pairing Correlation ◽  
Effective Interactions ◽  
Hartree Fock ◽  
Self Consistent ◽  
The Mean ◽  
Proton Pairing ◽  
Band Crossing

The high-spin state properties of the neutron–proton (np) residual effective interaction are analyzed in N = Z72 Kr , 76 Sr , and 80 Zr nuclei. The self-consistent microscopic Hartree–Fock–Bogoliubov (HFB) equations have been solved by employing monopole corrected two-body effective interaction. A band crossing is observed in 72 Kr nucleus at J = 14ℏ state with monopole corrected "HPU1" and "HPU2" effective interactions. The VAP–HFB theory suggests that the "4p–4h" excitations by np residual interaction are the essential ingredients of the mean-field description of the occurence of backbending in 72 Kr nucleus.

QUANTUM CORRECTIONS TO THE CRANKING MODEL

1992 ◽  
Vol 01 (01) ◽  
pp. 95-130 ◽  
Author(s):  
ABRAHAM KLEIN ◽  
NIELS R. WALET ◽  
G. DO DANG
Keyword(s):  
Degrees Of Freedom ◽  
Quantum Correction ◽  
Mean Field ◽  
Original System ◽  
Quantum Corrections ◽  
Transition Rates ◽  
Rotation Symmetry ◽  
Exchange Effects ◽  
Self Consistent ◽  
The Mean

A method is described for the restoration of translation or rotation symmetry to a system of fermions, starting from a self-consistent cranking solution and valid when either momentum or angular momentum is large enough so that semi-classical approximations are valid. The quantum fluctuations that restore the broken symmetry are described in terms of the particle-hole degrees of freedom of the original system rather than by mapping these variables onto a boson space, as in most previous work. Only the leading quantum correction to the mean field solution is worked out in detail. New results include the treatment of direct and exchange effects on an equal footing and a method for computing transition rates.

MEAN-FIELD THEORY FOR LAYERED HIGH-TEMPERATURE SUPERCONDUCTORS

1988 ◽  
Vol 02 (05) ◽  
pp. 1059-1065 ◽  
Author(s):  
D. Baeriswyl ◽  
T. Schneider
Keyword(s):  
High Temperature Superconductors ◽  
Mean Field Theory ◽  
Mean Field ◽  
Three Dimensional ◽  
Interlayer Coupling ◽  
Interlayer Spacing ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Pairing Mechanism ◽  
The Mean

Using the mean-field approximation we study a model for quasi-two-dimensional layered superconductors. The interlayer coupling, assumed to be mediated by a small electron hopping term, is found to leave Tc practically unaffected. Consequently, a three-dimensional pairing mechanism is required to explain the observed dependence of Tc on the average interlayer spacing in the Bi and Tl compounds.

scholarly journals MICROSCOPIC DETERMINATIONS OF FISSION BARRIERS (MEAN-FIELD AND BEYOND)

2007 ◽  
Vol 16 (02) ◽  
pp. 431-442 ◽  
Author(s):  
A. DOBROWOLSKI ◽  
H. GOUTTE ◽  
J.-F. BERGER
Keyword(s):  
Energy Barrier ◽  
Degrees Of Freedom ◽  
Mean Field ◽  
Fission Barrier ◽  
Hartree Fock ◽  
Potential Energy Landscape ◽  
New Energy ◽  
Collective Vibrations ◽  
The One ◽  
Least Energy

With a help of the selfconsistent Hartree-Fock-Bogoliubov (HFB) approach with the D1S effective Gogny interaction and the Generator Coordinate Method (GCM) we incorporate the transverse collective vibrations to the one-dimensional model of the fission-barrier penetrability based on the traditional WKB method. The average fission barrier corresponding to the least-energy path in the two-dimensional potential energy landscape as function of quadrupole and octupole degrees of freedom is modified by the influence of the transverse collective vibrations along the nuclear path to fission. The set of transverse vibrational states built in the fission valley corresponding to a successively increasing nuclear elongation produces the new energy barrier which is compared with the least-energy barrier. These collective states are given as the eigensolutions of the GCM purely vibrational Hamiltonian. In addition, the influence of the collective inertia on the fission properties is displayed, and it turns out to be the decisive condition for the possible transitions between different fission valleys.

Mean-Field Analysis of the Three-Band Hubbard Model

1998 ◽  
Vol 12 (27n28) ◽  
pp. 2831-2845 ◽  
Author(s):  
Yabin Yu ◽  
Guanghan Cao ◽  
Zhengkuan Jiao
Keyword(s):  
Electronic Structure ◽  
Hubbard Model ◽  
Singlet State ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Mean Field Approximation ◽  
Band Model ◽  
Spin Singlet ◽  
Half Filling ◽  
The Mean

A full three-band model for the CuO 2 plane of cuprates, which includes all the essential interaction — Cu-O and O-O hopping and the Coulomb repulsion on the Cu and O sites and between them, is considered. Its antiferromagnetic ground state for the half-filling is studied by using the mean field approximation. The electronic structure and the magnetic properties such as the densities of states, the energy spectra, the composition of holes (Cu or O character), the superexchange interaction and the magnetic moment are calculated and in general, our results are in agreement with the available experimental and other calculation results. Meanwhile, we find that the influence of the O-O hopping and Cu-O intrasite Coulomb repulsion on these properties is considerable. Our estimate of the energy of the spin singlet state above the antiferromagnetic background indicates that the lowest excitation state of the holes is the singlet state and give a charge-transfer energy in agreement with the experiment. We also discuss the hole-doping to the antiferromagnetic background and find the mean field approach invalid. Finally, based on the electronic structure at the half-filling, en effective one-band Hubbard model is presented and the effective parameters are close to the values given by the computation on the clusters.

scholarly journals 1/Nc EXPANSION FOR THE PARTITION FUNCTION IN FOUR-FERMION MODELS

1996 ◽  
Vol 11 (19) ◽  
pp. 1579-1587 ◽  
Author(s):  
A. BARDUCCI ◽  
R. CASALBUONI ◽  
M. MODUGNO ◽  
G. PETTINI ◽  
R. GATTO
Keyword(s):  
Partition Function ◽  
Low Temperatures ◽  
Degrees Of Freedom ◽  
Mean Field ◽  
Field Approximation ◽  
Functional Integral ◽  
Mean Field Approximation ◽  
Thermodynamical Potential ◽  
Low Mass ◽  
The Mean

We present a derivation of the bosonic contribution to the thermodynamical potential of four-fermion models by means of a 1/N c -expansion of the functional integral defining the partition function. This expansion turns out to be particularly useful in correcting the mean field approximation especially at low temperatures, where the relevant degrees of freedom are low-mass bosonic excitations (pseudo-Goldstones).

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