共查询到20条相似文献,搜索用时 15 毫秒
1.
The asymmetric Hubbard model with hopping integrals
dependent on an electron spin (particle sort) is studied using an
approximate analytic method within the dynamical mean-field
theory. The equations of motion for Hubbard operators followed by
projecting and different-time decoupling are used for solving the
single-site problem. Particle spectra are investigated at
half-filling within various approximations (Hubbard-I,
alloy-analogy and a generalization of the Hubbard-III
approximation). At half-filling these approximations can describe
only continuous gap opening in the spectrum.
The approach is used to describe the system between two limit
cases (the Falicov-Kimball model and the standard Hubbard model)
with continuous transition where Uc is dependent on
the value of hopping parameters of different particles. 相似文献
2.
J. M.P. Carmelo K. Penc 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):477-499
We introduce a method that allows the evaluation of general expressions for the spectral
functions of the one-dimensional Hubbard model for all values of the on-site
electronic repulsion U. The spectral weights are expressed in terms of pseudofermion
operators such that the spectral functions can be written as a convolution of
pseudofermion dynamical correlation functions. Our results are valid for all finite
energy and momentum values and are used elsewhere in the study of the unusual
finite-energy properties of quasi-one-dimensional compounds and the new quantum systems
of ultra-cold fermionic atoms on an optical lattice. 相似文献
3.
W. Fettes I. Morgenstern 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):635-639
We perform numerical simulations of the Hubbard model using the projector Quantum Monte Carlo method. A novel approach for
finite size scaling is discussed. We obtain evidence in favor of d-wave superconductivity in the repulsive Hubbard model. For U=4, is roughly estimated as K.
Received 8 September 1998 相似文献
4.
5.
The one-dimensional Hubbard model is integrable in the sense that it has an infinite family of conserved currents. We explicitly construct a ladder operator which can be used to iteratively generate all of the conserved current operators. This construction is different from that used for Lorentz invariant systems such as the Heisenberg model. The Hubbard model is not Lorentz invariant, due to the separation of spin and charge excitations. The ladder operator is obtained by a very general formalism which is applicable to any model that can be derived from a solution of the Yang-Baxter equation. 相似文献
6.
M. Noga 《Czechoslovak Journal of Physics》1992,42(8):823-841
The representation of the electron field operators separating charge from spin and providing transmutations between spin and isospin quantum numbers has been derived for any dimension. In this representation the interaction term in the Hubbard model is expressed in a bilinear form of quasiparticle field operators. The quasiparticles are spinless fermions with the electron electric charge. The consequence of this representation is that superconductivity in the strong coupling Hubbard model is due to odd wave pairings of electrons.The author expresses his sincere gratitude to Professor S. Stenholm for discussions and for the warm hospitality at the Research Institute for Theoretical Physics, University of Helsinki where this work has began. He would especially like to thank Professor C. Cronström who played an important role in the early and final stages of this work. Professor Anderson is acknowledged for providing the author with two chapters of his book (not yet published) quoted in the Discussion. 相似文献
7.
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9.
We present a series of rigorous examples of the Kondo lattice model that exhibit full ferromagnetism in the ground state.
The models are defined in one-, two- and three-dimensional lattices, and are characterized by a range of hopping terms, specific
electron filling, and large ferromagnetic coupling. Our examples show that a sufficient strong but finite exchange coupling
between conduction electrons and localized spins could overcome the competition from mobility of a finite density of electrons
and drive the system from a paramagnetic phase to a ferromagnetic phase. We also establish a relation of ferromagnetism between
the Hubbard model and Kondo lattice model. Meanwhile some rigorous results on ferromagnetism in the corresponding Hubbard
model are presented.
Received: 10 September 1997 / Revised: 15 October 1997 / Accepted: 17 October 1997 相似文献
10.
M. Noga 《Czechoslovak Journal of Physics》1993,43(12):1223-1239
It is shown that the field operators of an electron system on a lattice can be decomposed into direct products of two kinds of operators acting in two separate Hilbert spaces. The Hilbert space of electron states thus becomes a direct product of two Hilbert spaces. By this fact a certain class of electron systems exhibits a formal separation of charge and spin degrees of freedom into two kinds of elementary excitations. A typical example of such a system is given by the Hubbard model. The separation of charge and spin resulting from the new representation of the field operators can be considered as a rigorous realization and generalization of an idea expressed by Anderson concerning the separation of spin and charge degrees of freedom in strongly correlated electron systems. The new representation of electron field operators implies the existence of a localU(2) gauge symmetry in the theory. The theory of superconductivity based on the Hubbard model is then represented by a non-abelian gauge field theory.Dedicated to the memory of my teacher and friend Professor Jozef Kvasnica.The main part of this work has been done during the author stay at the Research Institute for Theoretical Physics, University of Helsinki. The author expresses this sincere gratitude to Prof. C. Cronström, who played an important role in completing this work. 相似文献
11.
运用约束路径量子蒙特卡罗方法,对二维、三带Hubbard模型中的环形电流相进行数值模拟。在数值模拟过程中定义了表征环流相的不同算符及其关联函数,并且选用合理的模型Hamiltonian量中的参数。通过模拟发现,对应于闭合环形的关联函数在相同距离上要比其他所有没有闭合的关联函数大得多,因此证明在三带Hubbard模型中存在环形电流相。 相似文献
12.
C. F. Lo 《Il Nuovo Cimento D》1991,13(1):127-130
Summary We have investigated the ground state of a single hole in the half-filled Hubbard model on a 2D square lattice using the coupled-cluster
method. In particular we obtained an analytical expression of the hole energy dispersion function ɛ(k) which is consistent with earlier studies on thet-J model in the strong-coupling limit. An appreciable discrepancy on the hole energy bandwidth is, however, observed between
the Hubbard model and thet-J model. We believe that this discrepancy is due to the absence of the three-site interaction term in thet-J model. 相似文献
13.
Projection operators are incorporated in the canonical transformation to derive an analytical infinite series of a degenerate perturbation expansion. The theory is used to calculate the ground state energy of a half-filled s-band Hubbard model to seventh order. 相似文献
14.
Oliver Hammrich 《Zeitschrift für Physik B Condensed Matter》1993,91(4):501-505
For temperature zero the effects of disorder for interacting bosons are considered. The disorder induced superfluid-insulator transition in thed-dimensional disordered Bogoliubov model is discussed. Results for a short-range and a long-range random potential are given. For short-range disorder we argue that ford<4 arbitrarily small disorder localizes the Bose condensate for vanishing interaction potential. Ford>4 a certain strength of the disorder potential is necessary in order to localize the condensate. For the three-dimensional Bogoliubov model our results are in agreement with a recent calculation. We compare our theoretical predictions with numerical experiments for a disordered boson Hubbard model. 相似文献
15.
Z.G. Koinov 《Physica C: Superconductivity and its Applications》2010,470(2):144-148
We transform the quartic Hubbard terms in the extended Hubbard model to a quadratic form by making the Hubbard–Stratonovich transformation for the electron operators. This transformation allows us to derive exact results for mass operator and charge–charge and spin–spin correlation functions for s-wave superconductivity. We discuss the application of the method to the d-wave superconductivity. 相似文献
16.
P. M.R. Brydon M. Gulácsi A. Bussmann-Holder 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):73-81
We present a non-perturbative study of an extended Falicov-Kimball model in
one
dimension. Working within the binary alloy interpretation, we include the
spin of the itinerant electrons and a Hubbard interaction to model the
inter-electron correlations. We derive an effective Ising model for the atomic
configuration in order to show how the Hubbard term affects the stability
of the phase separated states. Furthermore, we investigate the competition
between the Mott insulator state of the itinerant electrons and the
checkerboard phase of the spinless Falicov-Kimball model. 相似文献
17.
Anil Khurana 《Zeitschrift für Physik B Condensed Matter》1994,95(3):287-289
The Hubbard solution to the Hubbard model showed a non-trivial metal-insulator transition. The value of the one-particle density of states at the Fermi energy in that solution decreased continuously with increasing value of the Hubbard interaction and vanished at a critical value of the interaction. Such a solution is derived from a planar model, as an approximation to the exact construction of the model's one-particle Green function. 相似文献
18.
J.E. Espinosa O. Navarro M. Avignon 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):9-16
A real-space method has been introduced to study the pairing problem within the generalized Hubbard Hamiltonian. This method
includes the bond-charge interaction term as an extension of the previously proposed mapping method [1] for the Hubbard model.
The generalization of the method is based on mapping the correlated many-body problem onto an equivalent site- and bond-impurity
tight-binding one in a higher dimensional space, where the problem can be solved exactly. In a one-dimensional lattice, we
analyzed the three particle correlation by calculating the binding energy at the ground state, using different values of the
bond-charge, the on-site (U) and the nearest-neighbor (V) interactions. A pairing asymmetry is found between electrons and holes for the generalized hopping amplitude, where the
hole pairing is not always easier than the electron case. For some special values of the hopping parameters and for all kinds
of interactions in the Hubbard Hamiltonian, an analytical solution is obtained.
Received 21 January 2000 and Received in final form 18 July 2000 相似文献
19.
We extend the Green function approach to quantum transport through an anisotropic molecular magnet system with the help of Hubbard operators. Based on the single molecular magnet model, we reformulate the large spin and the total Hamiltonian in the language of Hubbard operators and obtain analytical expressions of the retarded Green function in sequential tunneling and Kondo regimes. In addition to this, we show the connection of our method to the master equation method in sequential regime and discuss a simple isotropic case in Kondo regime, in which we find a three-peak Kondo structure, a feature characterizing the isotropic exchange interaction between the localized electron and large spin. 相似文献
20.
Yang's η pairing operator is generalized to explore off-diagonal long-range order in the Hubbard bilayer with an arbitrary chemical potential. With this operator and a constraint condition on annihilation and creation operators, we construct explicitly eigenstates which possess simultaneously three kinds of off-diagonal long-range order, i.e., the intralayer one and the interlayer one for on-site pairing, and that for interlayer nearest-neighbor pairing. As in the simple Hubbard model there is also an SO(4) symmetry, with the generators properly defined. A sufficient condition leads to at least one of the above three kinds of off-diagonal long-range order. A constraint relation among different kinds of off-diagonal long-range order is also given. There exists a triplet of collective modes if the U(1) symmetry of a subgroup is spontaneously broken. 相似文献