共查询到20条相似文献,搜索用时 0 毫秒
1.
Strong-coupling theory of two dimensional large bipolarons in elliptical quantum dots 总被引:1,自引:0,他引:1
R.T. Senger A. Erçelebi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):253-260
In the limit of strong electron-phonon coupling, we analyze the stability of two dimensional bipolarons in a two-axis elliptic
potential well of harmonic boundaries. The confined two-polaron wavefunction adopted here makes the electrons to form either
a bipolaronic bound state or go into a composite state of two separated polarons bounded inside the same potential well. The
methodology involves the mean polaron-polaron separation treated as an adjustable parameter to be determined variationally.
By tuning the barrier slopes of the confining potential we obtain an explicit tracking of the criterion for bipolaron stability
encompassing the particular cases of a two dimensional circular dot or a planar strip-like quantum well wire. We observe that,
while an increased degree of confinement enhances bipolaronic stability, the effect of anisotropy is to inhibit bipolaron
formation.
Received 30 July 2001 and Received in final form 28 January 2002 相似文献
2.
Q. Yuan T. Nunner T. Kopp 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(1):37-42
Based on a half-filled two-dimensional tight-binding model with nearest-neighbour and next nearest-neighbour hopping the effect
of imperfect Fermi surface nesting on the Peierls instability is studied at zero temperature. Two dimerization patterns corresponding
to a phonon vector (π,π) are considered. It is found that the Peierls instability will be suppressed with an increase of next
nearest-neighbour hopping which characterizes the nesting deviation. First and second order transitions to a homogeneous state
are possible. The competition between the two dimerized states is discussed.
Received 22 December 2000 相似文献
3.
Qingshan Yuan 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):281-288
In this paper we study Peierls instabilities for a half-filled two-dimensional tight-binding model with nearest-neighbour
hopping t and next nearest-neighbour hopping t' at zero and finite temperatures. Two dimerization patterns corresponding to the same phonon vector (π,π) are considered to
be realizations of Peierls states. The effect of imperfect nesting introduced by t' on the Peierls instability, the properties of the dimerized ground state, as well as the competition between two dimerized
states for each t' and temperature T, are investigated. It is found: (i). The Peierls instability will be frustrated by t' for each of the dimerized states. The Peierls transition itself, as well as its suppression by t', may be of second- or first-order. (ii). When the two dimerized states are considered jointly, one of them will dominate
the other depending on parameters t' and T. Two successive Peierls transitions, that is, the system passing from the uniform state to one dimerized state and then to
the other may take place with decrease of temperature. Implications of our results to real materials are discussed.
Received 31 July 2001 相似文献
4.
E.Ya. Sherman C. Ambrosch-Draxl 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):323-328
We consider changes in the electron-phonon coupling in high-T
c
cuprates caused by site-selective oxygen isotope substitution. Contrary to the total substitution, the site-selective replacement
influences the coupling constant for each phonon mode due to the induced changes in the phonon eigenvectors. The relative
changes for some modes can be larger than 100%. The measured properties sensitive to these changes are discussed.
Received 9 August 2001 and Received in final form 11 January 2002 相似文献
5.
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
6.
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
7.
Li Zhang Hong-Jing Xie Chuan-Yu Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):577-582
Within the framework of the dielectric continuum model, interface optical(IO) and surface optical(SO) phonon modes and the
Fr?hlich electron-IO (SO) phonon interaction Hamiltonian in a multi-shell spherical system were derived and studied. Numerical
calculation on CdS/HgS/H2O and CdS/HgS/CdS/H2O spherical systems have been performed. Results reveal that there are two IO modes and one SO mode for the CdS/HgS/H2O system, one SO mode and four IO modes whose frequencies approach the IO phonon frequencies of the single CdS/HgS heterostructure
with the increasing of the quantum number l for CdS/HgS/CdS/H2O. It also showed that smaller l and SO phonon compared with IO phonon, have more significant contribution to the electron-IO (SO) phonon interaction.
Received 16 October 2001 and Received in final form 23 January 2002 Published online 25 June 2002 相似文献
8.
D. Hennig 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(3):419-425
We study localization in polymer chains modeled by the nonlinear discrete Schr?dinger equation (DNLS) with next-nearest-neighbor
(n-n-n) interaction extending beyond the usual nearest-neighbor exchange approximation. Modulational instability of plane
carrier waves is discussed and it is shown that localization gets amplified under the influence of an enhanced interaction
radius. Furthermore, we construct exact localized solitonlike solutions of the n-n-n interaction DNLS. To this end the stationary
lattice system is cast into a nonlinear map. The homoclinic orbits of unstable equilibria of this map are attributed to standing
solitonlike solutions of the lattice system. We note that in comparison with the standard next-neighbor interaction DNLS which
bears only one type of static soliton-like states (either staggering or unstaggering) the one with n-n-n interaction radius
can support unstaggering as well as staggering stationary localized states with frequencies lying above respectively below
the linear band. Generally, the stronger the n-n-n interaction on the DNLS lattice the smaller are the maximal amplitudes
of the standing solitonlike solutions and the less rapid are their exponential decays.
Received 4 October 2000 相似文献
9.
B.H. Wu J.C. Cao G.Q. Xia H.C. Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):9-14
A detailed calculation of interface phonon assisted electron intersubband transition in double GaAs/AlGaAs quantum well structure
is presented. Our calculation concentrates on the lowest two subbands which can be designed to be in resonance with a given
interface phonon mode. Various phonon mode profiles display quasi-symmetric or quasi-antisymmetric shapes. The quasi-antisymmetric
phonon modes give rise to much larger transition rates than those assisted by quasi-symmetric ones. The transition rate reaches
a maximum when the subband separation coincides with a given phonon mode energy. The calculation procedure presented here
can be easily applied to the design and simulation of other low dimensional semiconductor structures, such as quantum cascade
lasers.
Received 22 December 2002 Published online 23 May 2003
RID="a"
ID="a"e-mail: bhwu@263.net 相似文献
10.
L. Jacak P. Machnikowski J. Krasnyj P. Zoller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):319-331
Carrier-phonon interaction in semiconductor quantum dots leads to three classes of phenomena: coherent effects (spectrum reconstruction)
due to the nearly-dispersionless LO phonons, incoherent effects (transitions) induced by acoustical phonons and dressing phenomena,
related to non-adiabatic, sub-picosecond excitation. Polaron spectra, relaxation times and dressing-related decoherence rates
are calculated, in accordance with experiment.
Received 30 August 2002 / Received in final form 25 November 2002 Published online 28 January 2003 相似文献
11.
Our recent experiments show that arrays of underdamped Josephson junctions radiate coherently only above a threshold number of junctions switched onto the radiating state. For each junction, the radiating state is a resonant step in the current-voltage characteristics due to the interaction between the junctions in the array and an electromagnetic cavity. Here we show that a model of a one-dimensional array of Josephson junctions coupled to a resonator can produce many features of the coherent be havior above threshold, including coherent radiation of power and the shape of the array current-voltage characteristic. The model also makes quantitative predictions about the degree of coherence of the junctions in the array. However, in this model there is no threshold; the experimental below-threshold region behavior could not be reproduced.Received: 11 April 2003, Published online: 23 July 2003PACS:
74.50.+r Tunneling phenomena; point contacts, weak links, Josephson
effects -
85.25.-j Superconducting devices 相似文献
12.
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
13.
D. Rönnow L.F. Lastras-Martínez M. Cardona 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):29-35
Within the past years the optical excitations of electrons have been measured for semiconductor samples of different isotope
compositions. The isotope shift observed have been compared with calculations of the effects of electron-phonon interaction
on the electronic band structure. While qualitative agreement has been obtained, some discrepancies remain especially concerning
the E1 and transitions. We have remeasured the effect of isotope mass on the E1 and transitions of germanium with several isotopic compositions. The results, obtained by means of spectroscopic ellipsometry,
confirm that the real part of the gap self-energies induced by electron-phonon interaction is larger than found from band
structure calculations, while the imaginary part agrees with those calculations, which are based on a pseudopotential band
structure and a bond charge model for the lattice dynamics. Our results agree with predictions based on the measured temperature
dependence of the gaps. We compare our data for E1 and with results for the lowest direct (E0) and indirect (Eg) gaps. The measured values of and increase noticeably with increasing isotope mass. Similar effects have been observed in the temperature dependence of in and . A microscopic explanation for this effect is not available.
Received: 6 March 1998 / Revised: 27 April 1998 /
Accepted: 15 May 1998 相似文献
14.
A. Fledderjohann K.-H. Mütter 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):211-218
We investigate the influence of energetic disorder, viscous damping and an external field on the electron transfer (ET) in
DNA. The double helix structure of the λ-form of DNA is modeled by a steric oscillator network. In the context of the base-pair
picture two different kinds of modes representing twist motions of the base pairs and H-bond distortions are coupled to the
electron amplitude. Through the nonlinear interaction between the electronic and the vibrational degrees of freedom localized
stationary states in the form of standing electron-vibron breathers are produced which we derive with a stationary map method.
We show that in the presence of additional energetic disorder the degree of localization of such breathers is enhanced. It
is demonstrated how an applied electric field initiates the long-range coherent motion of breathers along the bases of a DNA
strand. These moving electron-vibron breathers, absorbing energy from the applied field, sustain energetic losses due to the
viscous friction caused by the aqueous solvent as well as the impact of a moderate amount of energetic disorder. Moreover,
it is illustrated that with the choice of the amplitude and frequency of the external field, the breather can be steered to
a desired lattice position achieving control of the ET.
Received 5 July 2002 Published online 29 November 2002 相似文献
15.
B.S. Kandemir T. Altanhan 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):517-526
We investigate the stability condition of large bipolarons confined in a parabolic potential containing certain parameters
and a uniform magnetic field. The variational wave function is constructed as a product form of electronic parts, consisting
of center of mass and internal motion, and a part of coherent phonons generated by Lee-Low-Pines transformation from the vacuum.
An analytical expression for the bipolaron energy is found, from which the ground and excited-state energies are obtained
numerically by minimization procedure. The bipolaron stability region is determined by comparing the bipolaron energy with
those of two separate polarons, which is already calculated within the same approximation. It is shown that the results obtained
for the ground state energy of bipolarons reduce to the existing works in zero magnetic field. In the presence of a magnetic
field, the stability of bipolarons is examined, for three types of low-dimensional system, as function of certain parameters,
such as the magnetic-field, the electron-phonon coupling constant, Coulomb repulsion and the confinement strength. Numerical
solutions for the energy levels of the ground and first excited states are examined as functions of the same parameters.
Received 7 March 2002 and Received in final form 22 April 2002 Published online 25 June 2002 相似文献
16.
S. Fratini D. Feinberg M. Grilli 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):157-165
The phase diagram of half-doped manganite systems of formula A
0.5
A
′
0.5MnO3 is investigated within a single-orbital model incorporating magnetic double-exchange and superexchange, together with intersite
Coulomb and electron-lattice interactions. Strong Jahn-Teller and breathing mode deformations compete together and result
in shear lattice deformations. The latter stabilize the charge-ordered CE-type phase, which undergo first-order transitions
with temperature or magnetic field to either Ferromagnetic metallic or Paramagnetic insulating phases. An essential feature
is the self-consistent screening of Coulomb and electron-phonon interactions in the ferromagnetic phase.
Received 28 November 2000 相似文献
17.
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
18.
Yamada H Starikov EB Hennig D Archilla JF 《The European physical journal. E, Soft matter》2005,17(2):149-154
We numerically investigate localization properties of electronic states in a static model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with realistic parameters obtained by quantum-chemical calculation. The randomness in the on-site energies caused by the electron-phonon coupling is completely correlated to the off-diagonal parts. In the single electron model, the effect of the hydrogen-bond stretchings, the twist angles between the base pairs and the finite system size effects on the energy dependence of the localization length and on the Lyapunov exponent are given. The localization length is reduced by the influence of the fluctuations in the hydrogen bond stretchings. It is also shown that the helical twist angle affects the localization length in the poly(dG)-poly(dC) DNA polymer more strongly than in the poly(dA)-poly(dT) one. Furthermore, we show resonance structures in the energy dependence of the localization length when the system size is relatively small. 相似文献
19.
Electronic structure of three-dimensional quantum dots 总被引:1,自引:0,他引:1
T. Vorrath R. Blümel 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):227-235
We study the electronic structure of three-dimensional quantum dots using the Hartree-Fock approximation. The confining potential
of the electrons in the quantum dot is assumed to be spatially isotropic and harmonic. For up to 40 interacting electrons
the ground-state energies and ground-state wavefunctions are calculated at various interaction strengths. The quadrupole moments
and electron densities in the quantum dot are computed. Hund's rule is confirmed and a shell structure is identified via the addition energies and the quadrupole moments. While most of the shell structure can be understood on the basis of the
unperturbed non-interacting problem, the interplay of an avoided crossing and the Coulomb interaction results in an unexpected
closed shell for 19 electrons.
Received 5 November 2001 / Received in final form 12 November 2002 Published online 1st April 2003
RID="a"
ID="a"e-mail: vorrath@physnet.uni-hamburg.de 相似文献
20.
M. Manninen M. Koskinen S.M. Reimann B. Mottelson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):381-385
Exact many-body methods as well as current-spin-density functional theory are used to study the magnetism and electron localization
in two-dimensional quantum dots and quasi-one-dimensional quantum rings. Predictions of broken-symmetry solutions within the
density functional model are confirmed by exact configuration interaction (CI) calculations: In a quantum ring the electrons
localize to form an antiferromagnetic chain which can be described with a simple model Hamiltonian. In a quantum dot the magnetic
field localizes the electrons as predicted with the density functional approach.
Received 5 December 2000 相似文献