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1.
Optical properties of an interacting large polaron gas 总被引:1,自引:0,他引:1
V. Cataudella G. De Filippis G. Iadonisi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):17-22
The normal state conductivity, , of a system of interacting large polarons is calculated within the Random Phase approximation and some numerical results
are presented. The behaviour of the optical absorption as a function of the charge carrier density and of the temperature
is analyzed for different values of the electron-phonon coupling constant. It is shown that exhibits features similar to those observed in the infrared spectra of the cuprates.
Received 27 January 1999 相似文献
2.
Qinghu Chen Yuhang Ren Zhengkuan Jiao Kelin Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):59-63
The Feynman-Haken variational path integral theory is, for the first time, generalized to calculate the ground-state energy
of an electron coupled simultaneously to a Coulomb potential and to a longitudinal-optical (LO) phonon field in parabolic
quantum wires. It is shown that the polaronic correction to the ground-state energy is more sensitive to the electron-phonon
coupling constant than the Coulomb binding parameter and monotonically stronger as the effective wire radius decreases. We
apply our calculations to several semiconductor quantum wires and find that the polaronic correction can be considerably large.
Received 16 November 1998 相似文献
3.
J. Chatterjee M. Mitra A.N. Das 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):573-578
A two-site double exchange model with a single polaron is studied using a perturbation expansion based on the modified Lang-Firsov
transformation. The antiferromagnetic to ferromagnetic transition and the crossover from small to large polaron are investigated
for different values of the antiferromagnetic interaction (J) between the core spins and the hopping (t) of the itinerant electron. Effect of the external magnetic field on the small to large polaron crossover and on the polaronic
kinetic energy are studied. When the magnetic transition and the small to large polaron crossover coincide for some suitable
range of J/t, the magnetic field has very pronounced effect on the dynamics of polarons.
Received 1 June 2000 相似文献
4.
Polaronic effects on the energy levels of a double donor impurity in quantum wells in the presence of a magnetic field 总被引:3,自引:0,他引:3
Zi-xin Liu Zhen-jiang Lai Yong-chang Huang Ya Liu Guo-jun Cheng 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):347-350
In the presence of a magnetic field the Hamiltonian of the single or double polaron bound to a helium-type donor impurity
in semiconductor quantum wells (QWs) are given in the case of positively charged donor center and neutral donor center. The
couplings of an electron and the impurity with various phonon modes are considered. The binding energy of the single and double
bound polaron in AlxlGa 1-xlAs/GaAs/AlxrGa 1-xrAs QWs are calculated. The results show that for a thin well the cumulative effects of the electron-phonon coupling and the
impurity-phonon coupling can contribute appreciably to the binding energy in the case of ionized donor. In the case of neutral
donor the contribution of polaronic effects are not very important, however the magnetic field significantly modifies the
binding energy of the double donor. The comparison between the binding energies in the case of the impurity placed at the
quantum well center and at the quantum well edge is also given.
Received 16 February 1999 相似文献
5.
R.T. Senger A. Erçelebi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):439-446
In the limit of strong electron-phonon coupling, we provide a unified insight into the stability criterion for bipolaron formation
in low-dimensionally confined media. The model that we use consists of a pair of electrons immersed in a reservoir of bulk
LO phonons and confined within an anisotropic parabolic potential box, whose barrier slopes can be tuned arbitrarily from
zero to infinity. Thus, encompassing the bulk and all low-dimensional geometric configurations of general interest, we obtain
an explicit tracking of the critical ratio of dielectric constants below which bipolarons can exist.
Received 15 September 1999 and Received in final form 20 March 2000 相似文献
6.
S. Pokrant K.B. Whaley 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(2):255-267
We utilize a tight-binding model to study the effects of surface structure on electronic properties of CdSe clusters. The
model takes into account experimental information about structure and shape of the nanocrystals, as well as the nature and
distribution of capping ligands. The effects of both organic capping ligands and inorganic capping shells on the densities
of states (DOS) and on the single-particle absorption spectra of the clusters are calculated for various cluster shapes and
sizes, and are compared to results for clusters with truncated surfaces. For organic capping ligands, the effect of ligand
hybridization is investigated and a simple model of surface reconstruction is developed. Both ligand hybridization and surface
reconstruction are seen to have a major influence on the band edge electronic and optical properties. Inorganic capping shells
give rise to differential localization of valence and conduction band edge states, with the hole primarily confined to the
core region and the electron more evenly distributed over both core and shell.
Received 21 September 1998 / Received in final form: 15 December 1998 相似文献
7.
G. De Filippis V. Cataudella G. Iadonisi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):339-351
A simple approach to the many-polaron problem for both weak and intermediate electron-phonon coupling and valid for densities
much smaller than those typical of metals is presented. Within the model the total energy, the collective modes and the single-particle
properties are studied and compared with the available theories. It is shown the occurrence of a charge density wave instability
in the intermediate coupling regime.
Received 13 May 1998 相似文献
8.
Q.-H Chen Y.-H. Ren Z.-K Jiao 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):307-313
The general properties of one-dimensional large Fr?hlich polarons in motion are investigated with the previous extended coherent
states where two-phonon correlations are considered. As a result, the polaron energy, velocity, effective mass, and average
number of virtual phonons as a function the polaron total momentum are evaluated in a wide range of the coupling constant.
In addition, rich information about virtual phonons emitted by the electron in motion is obtained. More importantly, some
intrinsic features of 1D moving polarons are presented for the first time, which may also be suited to moving polarons in
more than one dimensions.
Received: 23 October 1997 / Revised and Accepted: 27 January 1998 相似文献
9.
10.
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
11.
M. Valín-Rodríguez A. Puente Ll. Serra 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(3):493-498
We present calculations within density functional theory of the ground state and collective electronic oscillations in small
two-dimensional quantum rings. No spatial symmetries are imposed to the solutions and, as in a recent contribution, a transition
to a broken symmetry solution in the intrinsic reference frame for an increasingly narrow ring is found. The oscillations
are addressed by using real-time simulation. Conspicuous effects of the broken symmetry solution on the spectra are pointed
out.
Received 6 April 2000 and Received in final form 9 June 2000 相似文献
12.
Resonant magnetopolaron effects in parabolic quantum wells in a tilted magnetic field 总被引:7,自引:0,他引:7
We study the resonant magnetopolaron effects in parabolic quantum wells in a tilted magnetic field. The renormalization of the first excited level, which is resonant with the ground state level plus one longitudinal-optical phonon is calculated at the resonance using an improved resonance approximation to be E= where is the polaron coupling constant. The exponent and the factor are calculated in dependence on the tilt angle of the magnetic field and the confinement energy. 相似文献
13.
P. Paci C. Grimaldi L. Pietronero 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):235-243
The inclusion of nonadiabatic corrections to the electron-phonon interaction leads to a strong momentum dependence in the
generalized Eliashberg equations beyond Migdal's limit. For a s-wave symmetry of the order parameter, this induced momentum dependence leads to an enhancement of when small momentum transfer is dominant. Here we study how the d-wave symmetry affects the above behavior. We find that the nonadiabatic corrections depend only weakly on the symmetry of
the order parameter provided that only small momentum scatterings are allowed for the electron-phonon interaction. In this
situation, We show that also for a d-wave symmetry of the order parameter, the nonadiabatic corrections enhance . We also discuss the possible interplay and crossover between s- and d-wave depending on the material's parameters.
Received 12 May 2000 相似文献
14.
L. Bányai H. Haug P. Gartner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):209-213
We compute numerically the time dependent retarded Green function of the polaron within the self-consistent RPA approximation.
The results show an approximately Gaussian behaviour at t=0 changing at later times its concavity to an exponential decay, as it has been predicted in the approximate form of an inverse
hyperbolic cosine function. The result contrasts with the non-selfconsistent RPA, where the exponential decay is only a transitory
behaviour and the asymptotics is rather oscillatory. Our conclusions are significant in the context of the quantum kinetics
with LO-phonons, where the transition from an intitially coherent scattering kinetics to a Markov kinetics with energy conservation
is controlled by the time behaviour of the retarded Green function.
Received: 18 September 1997 / Revised: 24 October 1997 / Accepted: 6 November 1997 相似文献
15.
A. La Magna R. Pucci 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):421-429
In this paper we have introduced a variational approach to investigate the ground state of a model which includes both the
Holstein electron-phonon interaction and the extended Hubbard electron-electron interaction. We have considered a variational
state for the phonon subsystem which generalizes the previous used forms. This state allows to take into account the possibility
of extended phonon mediated correlations. The effective electron Hamiltonian, which we have obtained, includes first and second
neighbor electron-electron interaction terms. We have treated exactly, through a Lanczos method, this effective model in the
one-dimensional case. We have applied our method to two Bechgaard salts and in these cases we have estimated the correlation
parameters. We have shown that the introduction of electron-phonon interaction allows an estimate of the on site U and nearest-neighbor V Coulomb repulsion, which are in agreement with the experimental optical spectra of the above mentioned two compounds.
Received: 30 October 1997 / Revised: 28 January 1998 / Accepted: 10 April 1998 相似文献
16.
L. Berthier J. L. Barrat J. Kurchan 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):635-641
We calculate analytically the conditions that establish the number of bound states in finite superlattices as a function of
the depth, width and separation of the wells. We consider a lattice of -wells and a set of rectangular wells. For this latter case, we show how for finite systems the energy levels already group
together in bands separated by gaps.
Received 24 April 1998 相似文献
17.
M. Geddo R. Ferrini G. Guizzetti M. Patrini S. Franchi P. Frigeri G. Salviati L. Lazzarini 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):19-24
We report on a photoreflectance investigation in the 0.8-1.5 eV photon energy range and at temperatures from 80 to 300 K on
stacked layers of InAs/GaAs self-assembled quantum dots (QDs) grown by Atomic-Layer Molecular Beam Epitaxy. We observed clear
and well-resolved structures, which we attribute to the optical response of different QD families. The dependence of the ground
state transition energy on the number of stacked QD layers is investigated and discussed considering vertical coupling between
dots of the same column. It is shown that Coulomb interaction can account for the observed optical response of QD families
with different morphology coexisting in the same sample.
Received 17 November 1999 相似文献
18.
R.S. Daries Bella 《Solid State Communications》2004,130(11):773-776
The ground state and a few excited state energies of a hydrogenic donor in a spherical quantum dot (GaAs in a GaAlAs matrix) are computed. While the 1s and the 2s-state energies behave normally for dots of all radii, the 2p0 and 2p± states are unbound for most of the radii of interest. It is predicted that a semiconductor quantum dot with a hydrogenic donor will exhibit photoconductivity for a low threshold wavelength ∼12 μm. The spin-orbit coupling gives a contribution of the order of 10−5 meV for both 2p0 and 2p± states. 相似文献
19.
Zu Wei Yan Xi Xia Liang 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):531-538
A variational theory is proposed to study the surface states of electrons in a semi-infinite ternary mixed crystal, by taking
the effect of electron-surface optical (SO) phonon interaction into account. The energy and the wave function of the electronic
surface-states are calculated. The numerical results of the energies of the surface states of the polarons and the self-trapping
energies are obtained as functions of the composition x and surface potential V0 for several ternary mixed crystal materials. The results show that the electron-phonon interaction lowers the surface-state
levels with the energies from several to scores of meV. It is also found that the self-trapping energy of the surface polaron
has a minimum at some middle value of the composition x. It is indicated that the electron-phonon coupling effect can not be neglected.
Received 4 January 1999 and Received in final form 7 January 2000 相似文献
20.
M. Capone M. Grilli W. Stephan 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):551-557
We investigate polaron formation in a many-electron system in the presence of a local repulsion sufficiently strong to prevent
local-bipolaron formation. Specifically, we consider a Hubbard-Holstein model of interacting electrons coupled to dispersionless
phonons of frequency . Numerically solving the model in a small one-dimensional cluster, we find that in the nearly adiabatic case , the necessary and sufficient condition for the polaronic regime to occur is that the energy gain in the atomic (i.e., extremely localized) regime overcomes the energy of the purely electronic system . In the antiadiabatic case, , polaron formation is instead driven by the condition of a large ionic displacement (g being the electron-phonon coupling). Dynamical properties of the model in the weak and moderately strong coupling regimes
are also analyzed.
Received 15 February 1999 相似文献