共查询到20条相似文献,搜索用时 31 毫秒
1.
P. Schlottmann A.A. Zvyagin 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):325-335
We consider the one-dimensional t
-
J model, which consists of electrons with spin S on a lattice with nearest neighbor hopping t constrained by the excluded multiple occupancy of the lattice sites and spin-exchange J between neighboring sites. The model is integrable at the supersymmetric point, J
=
t. Without spoiling the integrability we introduce an Anderson-like impurity of spin S (degenerate Anderson model in the limit), which interacts with the correlated conduction states of the host. The lattice model is defined by the scattering
matrices via the Quantum Inverse Scattering Method. We discuss the general form of the interaction Hamiltonian between the impurity and
the itinerant electrons on the lattice and explicitly construct it in the continuum limit. The discrete Bethe ansatz equations
diagonalizing the host with impurity are derived, and the thermodynamic Bethe ansatz equations are obtained using the string
hypothesis for arbitrary band filling as a function of temperature and external magnetic field. The properties of the impurity
depend on one coupling parameter related to the Kondo exchange coupling. The impurity can localize up to one itinerant electron
and has in general mixed valent properties. Groundstate properties of the impurity, such as the energy, valence, magnetic
susceptibility and the specific heat coefficient, are discussed. In the integer valent limit the model reduces to a Coqblin-Schrieffer impurity.
Received: 31 December 1997 / Accepted: 17 March 1998 相似文献
2.
O. Golinelli Th. Jolicœur E.S. Sørensen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):199-206
We study the magnetic excitation spectrum of the spin-1 chain with Hamiltonian .We focus on the range where the spin chain is in the gapped Haldane phase. The excitation spectrum and static structure factor is studied using
direct Lanczos diagonalization of small systems and density-matrix renormalization group techniques combined with the single-mode
approximation. The magnon dispersion has a minimum at until a critical value is reached at which the curvature (velocity) vanishes. Beyond this point, which is distinct from the VBS point and the Lifshitz
point, the minimum lies at an incommensurate value that goes smoothly to when approaches , the Lai-Sutherland point. The mode remains isolated from the other states: there is no evidence of spinon deconfinement
before the point .These findings explain recent observation of the behavior of the magnetization curve for .
Received 16 December 1998 相似文献
3.
T. Saikawa A. Ferraz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):17-22
Dynamical properties of the spin and charge response functions in the doped two-dimensional Hubbard model are calculated by
taking into account the drastic separation of the single-particle spectral function into the low-energy coherent and high-energy
incoherent parts due to the strong Coulomb interaction. We show that this evolution of the electronic states is the origin
of the broad and structureless feature in the charge response function. In the weak coupling regime the low-energy enhancement
of the spin excitation is produced which can be explained within the random phase approximation. However, for the larger interaction
close to the antiferromagnetic Stoner condition, the low-energy intensity of the spin excitation is suppressed.
Received: 25 September 1997 / Revised: 19 December 1997 / Accepted: 9 January 1998 相似文献
4.
A.A. Zvyagin 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):351-360
The behavior of charge and spin persistent currents in an integrable lattice ring of strongly correlated electrons with a
magnetic impurity is exactly studied. Our results manifest that the oscillations of charge and spin persistent currents are
similar to the ones, earlier obtained for integrable continuum models with a magnetic impurity. The difference is due to two
(instead of one) Fermi velocities of low-lying excitations. The form of oscillations in the ground state is “saw-tooth”-like,
generic for any multi-particle coherent one-dimensional models. The integrable magnetic impurity introduces net charge and
spin chiralities in the generic integrable lattice system, which determine the initial phase shifts of charge and spin persistent
currents. We show that the magnitude of the charge persistent current in the generic Kondo situation does not depend on the
parameters of the magnetic impurity, unlike the (magneto)resistivity of transport currents.
Received 30 January 2003 / Received in final form 12 March 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: zvyagin@fy.chalmers.se 相似文献
5.
M.T. Glossop D.E. Logan 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):513-525
We consider a symmetric Anderson impurity model with a soft-gap hybridization vanishing at the Fermi level, with r>0. Three facets of the problem are examined. First the non-interacting limit, which despite its simplicity contains much
physics relevant to the U>0case: it exhibits both strong coupling (SC) states (for r<1) and local moment states (for r>1), with characteristic signatures in both spectral properties and thermodynamic functions. Second, we establish general
conditions upon the interaction self-energy for the occurence of a SC state for U>0. This leads to a pinning theorem, whereby the modified spectral function is pinned at the Fermi level for any U where a SC state obtains; it generalizes to arbitrary r the pinning condition upon familiar in the normal r=0 Anderson model. Finally, we consider explicitly spectral functions at the simplest level: second order perturbation theory
in U, which we conclude is applicable for and r>1 but not for . Characteristic spectral features observed in numerical renormalization group calculations are thereby recovered, for both
SC and LM phases; and for the SC state the modified spectral functions are found to contain a generalized Abrikosov-Suhl resonance
exhibiting a characteristic low-energy Kondo scale with increasing interaction strength.
Received 26 August 1999 相似文献
6.
P. Nozières 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):447-457
The so called exhaustion problem occurs when few electrons have to screen many spins in a metal with magnetic impurities.
A singlet Fermi liquid ground state is possible only if all impurities are “isotropized” in such a way as to suppress their
entropy. That takes a time and the corresponding energy limits the Fermi liquid range. The present note explores that issue of time and energy scales, and it concludes that is much smaller than the single impurity Kondo temperature. Similarly the relevant energy scale is proportional to the number
of electrons. Recent results on the Mott metal insulator transition in infinite dimension are reconsidered in the light of
these results: controversies in that respect are shown to reduce to a simple physical question, with no firm answer as to
now.
Received: 5 May 1998 / Received in final form and Accepted: 29 July 1998 相似文献
7.
M. Sassetti B. Kramer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):357-367
The Raman spectra of quantum wires in the region of electronic intra-band excitations are investigated using one- and two-band
models based on the Luttinger approximation with spin. Structures related to charge and spin density modes are identified,
and analyzed with respect to their behavior with photon energy and temperature. It is found that the low-energy peaks in the
polarized spectra, close to resonance that are commonly assigned to “single particle excitations”, can be interpreted as the
signature of spin density excitations. A broad structure in the resonant depolarized spectrum is predicted above the frequency
of the spin density excitations. This is due to simultaneous but independent propagation of spin and charge density modes.
The results, when compared with experiment, show, that the electronic collective excitations of quantum wires at low energies
are characteristic for a non-Fermi liquid.
Received: 25 March 1998 / Accepted: 3 June 1998 相似文献
8.
The temperature-dependent optical conductivity of a Kondo insulator for different temperatures with impurity doping on the conduction band is studied within the U = ∞ Anderson lattice model in the framework of a slave-boson mean-field theory under the coherent potential approximation. The results show that the depletion of the optical conductivity in low-frequency region decreases with increasing of the temperature, and the system exhibits a transition between a low-temperature insulating phase and a high-temperature metallic phase. With increasing of the impurity concentration, the effect of the impurity scattering could result in a nearly temperature-independent gap behavior. The numerical results on the localization of the electron and its variation with temperature are also discussed with the help of optical sum rule. 相似文献
9.
K.-V. Pham M. Gabay P. Lederer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):573-576
Standard bosonization techniques lead to phonon-like excitations in a Luttinger liquid (LL), reflecting the absence of Landau
quasiparticles in these systems. Yet in addition to the above excitations some LL are known to possess solitonic states carrying
fractional quantum numbers (e.g. the spin 1/2 Heisenberg chain). We have reconsidered the zero modes in the low-energy spectrum of the Gaussian boson LL Hamiltonian
both for fermionic and bosonic LL: in the spinless case we find that two elementary excitations carrying fractional quantum
numbers allow to generate all the charge and current excited states of the LL. We explicitly compute the wavefunctions of
these two objects and show that one of them can be identified with the 1D version of the Laughlin quasiparticle introduced
in the context of the Fractional Quantum Hall effect. For bosons, the other quasiparticle corresponds to a spinon excitation.
The eigenfunctions of Wen's chiral LL Hamiltonian are also derived: they are quite simply the one dimensional restrictions
of the 2D bulk Laughlin wavefunctions.
Received 26 January 1999 and Received in final form 21 April 1999 相似文献
10.
11.
J. Dietel T. Koschny W. Apel W. Weller 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):439-445
We reconsider the theory of the half-filled lowest Landau level using the Chern-Simons formulation and study the grand-canonical
potential in the random-phase approximation (RPA). Calculating the unperturbed response functions for current- and charge-density
exactly, without any expansion with respect to frequency or wave vector, we find that the integral for the ground-state energy
converges rapidly (algebraically) at large wave vectors k, but exhibits a logarithmic divergence at small k. This divergence originates in the k-2 singularity of the Chern-Simons interaction and it is already present in lowest-order perturbation theory. A similar divergence
appears in the chemical potential. Beyond the RPA, we identify diagrams for the grand-canonical potential (ladder-type, maximally
crossed, or a combination of both) which diverge with powers of the logarithm. We expand our result for the RPA ground-state
energy in the strength of the Coulomb interaction. The linear term is finite and its value compares well with numerical simulations
of interacting electrons in the lowest Landau level.
Received: 19 February 1998 / Revised: 25 March 1998 / Accepted: 17 April 1998 相似文献
12.
M. Bocquet Th. Jolicoeur 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):47-52
We generalize the nonlinear sigma model treatment of quantum spin chains to cases including ferromagnetic bonds. When these
bonds are strong enough, the classical ground state is no longer the standard Néel order and we present an extension of the
known formalism to deal with this situation. We study the alternating ferromagnetic-antiferromagnetic spin chain introduced
by Hida. The smooth crossover between decoupled dimers and the Haldane phase is semi-quantitatively reproduced. We study also
a spin ladder with diagonal exchange couplings that interpolates between the gapped phase of the two-leg spin ladder and the
Haldane phase. Here again we show that there is a good agreement between DMRG data and our analytical results.
Received 6 September 1999 相似文献
13.
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
14.
G. Uimin Y. Kudasov P. Fulde A. Ovchinnikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):241-244
We discuss the effects of an applied magnetic field on the low-energy excitations in the low temperature phase of Yb4As3. We show also why the magnetic interaction of the Yb3+ ions is nearly of an isotropic Heisenberg spin-1/2 type. A small anisotropy due to an intrachain dipolar interaction leads
to the opening of a gap when a magnetic field is applied. The model agrees with available experimental data. Simple experiments
are suggested in order to further test the present theory.
Received 3 February 1999 相似文献
15.
16.
P. Bonville E. Vincent E. Bauer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):363-369
We present measurements in the YbCu5-xAlx series, down to the 50 mK range, using 170Yb M?ssbauer absorption spectroscopy and magnetisation measurements. In this series, the hybridisation between the Yb 4
f electrons and the conduction electrons is known to decrease as the Al content x increases. We apply the variational solution of the impurity Kondo problem to the interpretation of our data. We show that
the Kondo temperature can be derived from the measured 4
f quadrupole moment and, for the magnetically ordered compounds (), we obtain the exchange energy as a function of the Al content. Our findings are in general agreement with Doniach's model
describing the onset of magnetic ordering according to the relative values of the Kondo and exchange energy scales.
Received 16 April 1998 相似文献
17.
A.V. Nikolaev K.H. Michel 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):619-634
We have calculated the quantum quadrupolar interaction due to charge density fluctuations of localized 4f-electrons in Ce by taking into account the angular dependence, the degeneracy of the localized 4f
-orbitals and the spin-orbit coupling. The calculated crystal field of 4
f electronic states is in good agreement with neutron diffraction measurements. We show that orientational ordering of quantum
quadrupoles drives a phase transition at K which we assign with the transformation. In the phase the centers of mass of the Ce atoms still form a face centered cubic lattice. The theory accounts for the first order
character of the transition and for the cubic lattice contraction which accompanies the transition. The transition temperature
increases linearly with pressure. Our approach does not involve Kondo spin fluctuations as the significant process for the
phase transition.
Received 19 October 1998 相似文献
18.
M. Vojta R. Bulla 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):283-287
We consider a Kondo impurity coupled to a fermionic host with a power-law density of states near the Fermi level, ρ(ε) ∼ |ε|r, with exponent r < 0. Using both perturbative renormalization group (poor man's scaling) and numerical renormalization group methods, we analyze
the phase diagram of this model for ferromagnetic and antiferromagnetic Kondo coupling. Both sectors display non-trivial behavior
with several stable phases separated by continuous transitions. In particular, on the ferromagnetic side there is a stable
intermediate-coupling fixed point with universal properties corresponding to a fractional ground-state spin.
Received 18 February 2002 Published online 31 July 2002 相似文献
19.
H. Beckmann G. Bergmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):229-232
Thin Pd films with submonolayers of Ru are investigated by means of the anomalous Hall effect and weak localization. The anomalous
Hall resistance yields the magnetization of the film as a function of the applied magnetic field B. The susceptibility is only weakly temperature dependent. This suggests that the Pd/Ru is weakly ferromagnetic showing large
spin wave excitations. The maximum magnetization is found for a coverage of about 0.1 atomic layers of Ru. For larger coverages
the Ru moment decreases strongly. This is confirmed by the behavior of the electron dephasing rate determined from magnetoresistance
measurements.
Received: 9 July 1997 / Accepted: 6 November 1997 相似文献
20.
In this work, using the non-equilibrium Keldysh formalism, we study the effects of the electron–electron interaction and the electron-spin correlation on the non-equilibrium Kondo effect and the transport properties of the symmetric single impurity Anderson model (SIAM) at zero temperature by generalizing the self-consistent method of Singwi, Tosi, Land, and Sjolander (STLS) for a single-band tight-binding model with Hubbard type interaction to out of equilibrium steady-states. We at first determine in a self-consistent manner the non-equilibrium spin correlation function, the effective Hubbard interaction, and the double-occupancy at the impurity site. Then, using the non-equilibrium STLS spin polarization function in the non-equilibrium formalism of the iterative perturbation theory (IPT) of Yosida and Yamada, and Horvatic and Zlatic, we compute the spectral density, the current–voltage characteristics and the differential conductance as functions of the applied bias and the strength of on-site Hubbard interaction. We compare our spectral densities at zero bias with the results of numerical renormalization group (NRG) and depict the effects of the electron–electron interaction and electron-spin correlation at the impurity site on the aforementioned properties by comparing our numerical result with the order U2 IPT. Finally, we show that the obtained numerical results on the differential conductance have a quadratic universal scaling behavior and the resulting Kondo temperature shows an exponential behavior. 相似文献