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1.
C. Schneider G. Czycholl 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):43-50
We study the (spinless) Falicov-Kimball model extended by a finite band width (hopping t
f
) of the localized (f-) electrons in infinite dimensions in the weak-coupling limit of a small local interband Coulomb correlation U for half filling. In the case of overlapping conduction- and f-bands different kinds of ordered solutions are possible, namely charge-density wave (CDW) order, electronic ferroelectricity
(EFE) and electronic antiferroelectricity (EAFE). The order parameters are calculated as a function of the model parameters
and of the temperature. There is a first-order phase transition from the CDW-phase to the EFE- or EAFE-phase. The total energy
is calculated to determine the thermodynamically stable solution. The quantum phase diagrams are calculated. 相似文献
2.
A. K. Zhuravlev V. Yu. Irkhin M. I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):377-382
Using the numerical renormalization group method, the dependences on
temperature of the magnetic susceptibility χ(T) and specific heat C(T)
are obtained for the single-impurity Anderson model with inclusion of
d-f the Coulomb interaction. It is shown that the exciton effects
caused by this effect (charge fluctuations) can significantly change the
behaviour of C(T) in comparison with the standard Anderson model at
moderately low temperatures, whereas the behaviour of χ(T) remains nearly
universal. The ground-state and temperature-dependent renormalizations of the
effective hybridization parameter and f-level position caused by the
d-f interaction are calculated, and satisfactory agreement with the
Hartree-Fock approximation is derived. 相似文献
3.
S.G. Mishra P.A. Sreeram 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):287-291
Specific heat versus temperature curves for various pressures, or magnetic fields (or some other external control parameter) have been seen to
cross at a point or in a very small range of temperatures in many correlated fermion systems. We show that this behavior is
related to the possibility of existence of a quantum critical point. Vicinity to a quantum critical point in these systems
leads to a crossover from quantum to classical fluctuation regime at some temperature . The temperature at which the curves cross turns out to be near this crossover temperature. We have discussed the case of
the normal phase of liquid Helium three and the heavy fermion systems CeAl3 and UBe13 in detail within the spin fluctuation theory, a theory which inherently contains a low energy scale which can be identified
with . When the crossover scale is a homogeneous function of these control parameters there is always crossing at a point. We also
mention other theories exhibiting a low energy scale near a quantum critical point and discuss this phenomenon in those theories.
Received 25 June 1999 相似文献
4.
5.
V.Yu. Irkhin A.V. Zarubin 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):463-468
The Kondo divergences owing to interaction of current carriers with local moments in highly correlated electron systems are
considered within the Hubbard and s-d exchange models with infinitely strong on-site interaction, the many-electron Hubbard representation being used. The picture
of density of states containing a peak at the Fermi level is obtained. Various forms of the self-consistent approximation
are used. The problem of the violation of analytical properties of the Green's function is discussed. Smearing of the “Kondo”
peak owing to spin dynamics and finite temperatures is investigated.
Received 25 November 1999 and Received in final form 31 January 2000 相似文献
6.
R. Citro S. Cojocaru M. Marinaro 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):179-185
Phonon anomalies observed in various high Tc cuprates are
analyzed theoretically within the Hubbard-Holstein model in the
limit of strong local electron correlations and in presence of
long-range Coulomb interaction. The phonon self-energy is
evaluated by taking into account the charge collective modes that
become critical upon doping approaching an instability towards an
incommensurate charge density wave (ICDW) driven by electron
correlations. The doping dependence of phonon softening features
and the highly distinctive phonon self-energy dependence on the
wave vector agree with experiments. We discuss relevance of
dynamical corrections to the density correlation function to
achieve a sizeable bond-stretching phonon softening with a
kink-like profile away from the zone boundary. 相似文献
7.
L. Petit A. Svane W.M. Temmerman Z. Szotek 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):139-146
The electronic and magnetic properties of Pu monopnictides and monochalcogenides, PuX (X = N, P, As, Sb, Bi, O, S, Se, Te, Po), are studied using the self-interaction-corrected local spin-density approximation. This approach allows for an integer number of f-states to be localized, while the remaining f-electron degrees of freedom are available for band formation. By varying the relative proportions of localized and delocalized
f-states, the energetically most favourable (groundstate) configuration can be established. We show that the experimental data
can be interpreted in terms of the coexistence of both localized and delocalized f-states.
Received 10 August 2001 相似文献
8.
V.?Derzhko J.?J?drzejewski T.?Krokhmalskii 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(4):501-510
We discuss striped phases as a state of matter intermediate between
two extreme states: a crystalline state and a segregated state. We argue that
this state is very sensitive to weak interactions, compared to those
stabilizing a crystalline state, and to anisotropies.
Moreover, under suitable conditions a 2D system in a striped phase decouples
into (quasi) 1D chains. These observations are based on results of our studies
of an extension of a microscopic quantum model of crystallization, proposed originally
by Kennedy and Lieb. 相似文献
9.
S. K. Dhar P. Manfrinetti M. L. Fornasini P. Bonville 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):187-192
170Yb M?ssbauer spectroscopy, temperature dependent X-ray,
magnetisation and specific heat data are presented in the hexagonal
intermetallic YbAl3C3, in order to shed light on the isostructural
transition occurring near 80 K and
to investigate the electronic state of the Yb ion above and below the
transition. In the low temperature phase, we find that there occurs an atomic
rearrangement in the hexagonal unit cell, leading to a strong symmetry
lowering at the Yb site. We show that no magnetic ordering of the Yb3+
moments occurs down to 0.04 K, and we discuss this finding in terms of
4f-conduction electron hybridisation and geometric frustration. 相似文献
10.
11.
M.?Gam?a A.??lebarski H.?Rosner 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(4):483-494
Electronic structure of the compounds CeRhIn and CeRhSn have been studied by the X-ray photoemission spectroscopy (XPS) and
ab initio band structure calculations.
CeRhSn shows the non-Fermi liquid characteristics at low temperatures, while CeRhIn exhibits a Fermi-liquid ground state.
At ambient temperature the XPS data reveal an intermediate valence state of Ce ions in both systems. The Ce core-level XPS
spectra are very similar and indicate the strong coupling of the Ce 4f and the conduction band states (Δ ≈ 100 meV).
The valence band spectra we interpret with the help of ab initio calculations as well as using the results for the reference
compounds LaRhIn and LaRhSn.
The comparative analysis of the theoretical band structures and charge density plots reveal the changes in chemical bonding
and the hybridization between the Ce 4f and the other valence states introduced by the replacement of In by Sn atoms.
The more covalent character of the chemical bonding in the stannides is in line with the smaller thermal expansion. Finally,
for CeRhIn we found a typical temperature dependence of the crystal lattice, while CeRhSn shows distinct anomaly at about
120 K, presumably related to the change in planar Ce–Rh bonds. 相似文献
12.
S. Massidda R. Monnier E. Stoll 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):645-649
The electronic structure and the Fermi surface BaB6 are studied as a function of doping in a conventional bandstructure approach based on the local density approximation to
density functional theory (LDA). In particular it is shown that magnetic breakthrough can occur between the two sheets of
the Fermi surface disconnected by electron-hole mixing and the spin-orbit interaction. It is further suggested that angle-resolved
photoemission will see a single ellipse in the (100) plane for certain doping values, due to the finite energy/momentum resolution
of the method. Transport properties, computed within Bloch-Boltzmann theory, are also presented. The bare plasma energy is
found to be 0.6 eV in the stoichiometric compound.
Received 23 May 2000 相似文献
13.
14.
P. Farkašovský 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):209-215
A new numerical method is used to study the ground-state properties of the spinless Falicov-Kimball model in one and two dimensions.
The resultant solutions are used to examine the phase diagram of the model as well as possibilities for valence and metal-insulator
transitions. In one dimension a comprehensive phase diagram of the model is presented. On the base of this phase diagram,
the complete picture of valence and metal-insulator transitions is discussed. In two dimensions the structure of ground-state
configurations is described for intermediate interactions between f and d electrons. In this region the phase separation and metal-insulator transitions are found at low f-electron concentrations. It is shown that valence transitions exhibit a staircase structure.
Received 20 October 2000 相似文献
15.
G.?Urbanik T.?H?nke C.?Hess B.?Büchner A.?Ciszewski V.?Hinkov C. T.?Lin B.?Keimer 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(4):483-489
We performed scanning tunneling microscopy and spectroscopy on untwinned crystals of underdoped YBa2Cu3O7-
δ at δ = 0.4. A comprehensive statistical analysis of our topographic data indicates a doping dependent cleaving behavior of
this material. We find in particular that at δ = 0.4 the material primarily cleaves in multiples of one unit cell along the
c-axis with a high corrugation of the topmost layer. Our data suggest that the low temperature cleaving mainly results in
a disruption of the CuO chain layers involving a redistribution of the layer atoms onto the two cleaving planes. In a few instances, fractional
step heights (in terms of the c-axis lattice constant) are observed as well. Scanning tunneling spectroscopy reveals that
such fractional steps connect surfaces which differ significantly in their tunneling conductance. 相似文献
16.
Yu. O. Klymenko O. Shevtsov 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(2):203-209
Ab initio calculations based on the Density Functional Theory are carried out in order to investigate the incorporation of
iodine in uranium dioxide. The GGA+U approximation is used to describe the strong correlations of uranium 5f electrons. We
studied several defects that are likely to accommodate the incorporation of iodine in the material, such as uranium and oxygen
vacancies, divacancy and Schottky defects. We find the iodine atoms to be stable in a neutral Schottky defects, with an incorporation
energy of -1.3 eV. This result may account for the solubility of iodine in uranium dioxide observed experimentally. We also
notice that the incorporation of iodine involves steric and electronic contributions. The larger the defect iodine is incorporated
in, the lower is its incorporation energy. Besides, we find iodine to be charged -1, thus getting the stable electronic configuration
of rare gases. We also highlight the fact that the use of GGA+U increases the number of metastable states (non global energy
minima), compared to the LDA/GGA approximations. Consequently, special care has to be taken on the 5f electronic occupancies
in order to ensure that the absolute energy minimum has been reached. 相似文献
17.
Z. Kovacevic R. Hayn N.M. Plakida 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):487-495
In the framework of the cell-perturbation method for the original p-d model an effective two-band Hubbard model for the CuO2 plane with Zn impurities is derived. Zn impurities are modelled by Wannir oxygen one-hole states at vacant Cu sites. The model is based on the results of band structure calculations carried out
within the local-density approximation. Further reduction to an extended t-J model shows a large ferromagnetic superexchange interaction between the Cu spin with the nearest virtual oxygen spin in the
Zn cell.
Received 17 November 1998 相似文献
18.
J. Kurzyk W. Wójcik J. Spałek 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(3):385-398
The method used earlier for analysis of correlated nanoscopic systems is extended to infinite (periodic) s-band-like systems
described by the Hubbard model. The optimized single-particle Wannier wave functions contained in the parameters of the extended
Hubbard model (in the nearest-neghbor hopping (-t), in the magnitude of the intraatomic interaction U, and in other parameters) are determined explicitly in the correlated state for the electronic systems of various symmetries
and dimensions: Hubbard chain, square and triangular planar lattices, and the three cubic lattices (SC, BCC, FCC). In effect,
the evolution of the electronic properties as a function of interatomic distance R is obtained. The model parameters in most
cases do not scale linearly with the lattice spacing and hence, their solution as a function of microscopic parameters reflects
only qualitatively the system evolution. Also, the atomic energy changes with R and therefore should be included in the model
analysis. The solutions in one dimension (D = 1) can be analyzed both rigorously (by making use of the Lieb–Wu solution) and compared with the approximate Gutzwiller
treatments. In higher dimensions (D = 2 and 3) only the latter approach is possible to implement within the scheme. The renormalized single particle wave functions
are almost independent of the choice of the scheme selected to diagonalize the Hamiltonian in the Fock space in D = 1 case.
For dimensions D > 1 the qualitative behavior is independent of the structure considered. The wave-function size increases
above the Mott-Hubbard localization threshold and gradually reaches the atomic limit value. The method can be extended to
other approximation schemes, as stressed at the end. 相似文献
19.
F. Heidrich-Meisner G. B. Martins C. A. Büsser K. A. Al-Hassanieh A. E. Feiguin G. Chiappe E. V. Anda E. Dagotto 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(4):527-542
The numerical analysis of strongly interacting nanostructures
requires powerful techniques.
Recently developed methods, such as the time-dependent density matrix renormalization group (tDMRG) approach or the embedded-cluster
approximation (ECA), rely on the numerical solution of clusters of finite size. For the interpretation of numerical results,
it is therefore crucial to understand finite-size effects
in detail. In this work, we present a careful finite-size analysis for the examples of one quantum dot, as well as three serially
connected quantum
dots. Depending on “odd-even” effects, physically quite different
results may emerge from clusters that do not differ much in their size. We provide
a solution to a recent controversy over results obtained with ECA for three quantum dots.
In particular, using the optimum clusters discussed in this paper, the parameter range in which
ECA can reliably be applied is increased, as we show for the case of three quantum dots.
As a practical procedure, we propose that a comparison of results for static quantities against those of quasi-exact methods,
such as the ground-state density matrix renormalization group (DMRG) method or exact diagonalization,
serves to identify the optimum cluster type.
In the examples studied here, we find that to observe signatures of the Kondo effect in finite systems, the best clusters
involving dots and leads
must have a total z-component of
the spin equal to zero. 相似文献
20.
Shiping Feng Feng Yuan Weiqiang Yu 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):607-614
The c-axis charge dynamics of copper oxide materials in the underdoped and optimally doped regimes has been studied by considering
the incoherent interlayer hopping. It is shown that the c-axis charge dynamics for the chain copper oxide materials is mainly governed by the scattering from the in-plane fluctuation,
and the c-axis charge dynamics for the no-chain copper oxide materials is dominated by the scattering from the in-plane fluctuation
incorporating with the interlayer disorder, which would be suppressed when the holon pseudogap opens at low temperatures and
lower doping levels, leading to the crossovers to the semiconducting-like range in the c-axis resistivity and the temperature linear to the nonlinear range in the in-plane resistivity.
Received 29 July 1999 and Received in final form 24 January 2000 相似文献