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1.
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
2.
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
3.
H. Fehske D. Ihle J. Loos U. Trapper H. Büttner 《Zeitschrift für Physik B Condensed Matter》1994,94(1-2):91-100
On the basis of the Holstein-Hubbard model the formation of polarons at finite densities is investigated by means of a variational approach appropriate for describing squeezing and correlation effects. An effective Hubbard model for the polarons is derived, where the correlations are treated within the slave-boson saddlepoint approximation. For low enough phonon frequencies, with increasing coupling an abrupt self-trapping transition from light to heavy polarons is found. With increasing density the squeezing effect increases, and the transition is shifted to higher couplings. In the case of an effective Coulomb repulsion, the self-trapping transition is shifted to lower couplings with increasing Hubbard interaction, and the effective polaron mass below the transition is enhanced. In the heavy polaron regime, the frequency-dependent polaron hopping conductivity is calculated. There occur qualitative finite-density and correlation effects on the zero-temperature absorption spectrum which are discussed with respect to their possible relevance to the midinfrared absorption in high-T
c
superconductors. 相似文献
4.
A theory of excitonic polarons in semiconductor quantum wells is presented. Using a unitary transformation, we have diagonalized the exciton-phonon interaction operator in a quasi-two-dimensional system partially and then calculated the ground-state energy of an excitonic polaron. We have numerically evaluated the energy gap shift and effective mass of an excitonic polaron. We have numerically evaluated the energy gap shift and effective mass of an excitonic polaron in GaAs-Al
x
Ga1–x
As systems. The results obtained here indicate that the polaronic effect is significant in the case of the light hole excitons in quantum wells of small well widths. 相似文献
5.
Y.H. Ren Q.H. Chen Y.B. Yu Z.A. Xu W.B. Shao Z.K. Jiao 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):651-656
Within the framework of the second-order Rayleigh-Schr?dinger perturbation theory, we investigate the effects of the interaction
of the electron and longitudinal-optical phonons in two-dimensional semiconductive quantum dots with respect to a general
potential. We propose a simple expression for the ground state energy, and compare it with those obtained by Landau-Pekar
strong coupling theory. It is shown both analytically and numerically that the results obtained from the second-order Rayleigh-Schr?dinger
perturbation theory could be better than those from Landau-Pekar strong coupling theory when the coupling constant is sufficiently
small. Moreover, some interesting problems, such as polarons in quasi-one-dimensional quantum wires, and quasi-zero-dimensional
asymmetric or symmetric quantum dots can be easily discussed only by taking different limits. After the numerical calculations,
we find that there exists a simple dimensional scaling and symmetry relation for the ground state polaron energy. Furthermore,
we apply our results to some weak-coupling polar semiconductors such as GaAs, CdS. It is shown that the polaronic effects
are found to be quiet appreciable if the confinement lengths and smaller than a few nanometers.
Received: 3 December 1997 / Revised: 6 July 1998 / Accepted: 17 September 1998 相似文献
6.
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
7.
Q.S. Hu H. Zheng 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):255-262
A new perturbation approach is developed for single- and many-electron Holstein model in one-, two-, and three-dimension.
The results show that this approach has a good agreement with the Migdal theory in the adiabatic regime when the coupling
is moderate (λ < 1), but with the Lang-Firsov theory in the antiadiabatic regime ( ω/W≫ 1). In the intermediate region, our approach can describe the transition from a large-polaron Fermi-liquid to the small-polaron,
and this transition may be discontinuous in adiabatic regime, which means a phase transition appears in many-electron system.
In single-electron case, we eliminate the abrupt transition using the degenerate perturbation theory, and the calculated ground
state energy and effective mass are successfully compared with those of previous authors. Besides, the method has the advantage
of requiring little computational effort.
Received 27 December 2001 / Received in final form 8 April 2002 Published online 31 July 2002 相似文献
8.
A. Paolone P. Roy A. Pimenov A. Loidl A.A. Mukhin A.M. Balbashov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):245-250
The optical conductivity of La0.85Sr0.15MnO3 single crystals was studied by means of submillimeter and infrared spectroscopy for frequencies cm-1 and temperatures 10 K <
T
<300 K. The submillimeter conductivity follows the temperature dependence of the dc-data. The phonon spectrum of La0.85Sr0.15MnO3 changes considerably below K revealing a structural phase transition induced by charge or orbital order. At T
=10 K a number of phonon modes can be identified in addition to the room-temperature spectrum. The optical conductivity () in the mid-infrared reveals the characteristics of small polaron absorption. Below the magnetic ordering temperature the
polaron binding energy is highly reduced, but the onset of charge order interrupts the formation of free charge carriers with
a Drude-like behavior. The frequency and temperature dependence of in this regime qualitatively resembles the small polaron predictions by Millis et al. (Phys. Rev. B 54, 5405 (1996)).
Received 5 November 1999 相似文献
9.
Interface polarons in a realistic heterojunction potential 总被引:9,自引:0,他引:9
S.L. Ban J.E. Hasbun 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):453-461
The ground states of interface polarons in a realistic heterojunction potential are investigated by considering the bulk and
the interface optical phonon influence. A self-consistent heterojunction potential is used and an LLP-like method is adopted
to obtain the polaron effect. The numerical computation has been done for the Zn1-xCdxSe/ZnSe system to obtain the polaron ground state energy, self energy and effective mass parallel to the interface. A simplified
coherent potential approximation is developed to obtain the parameters of the ternary mixed crystal and the energy band offset
of the heterojunction. It is found that at small Cd concentration the bulk longitudinal optical phonons give the main contribution
for lower areal electron densities, whereas the interface phonon contribution is dominant for higher areal electron densities.
The interface polaron effect is weaker than the effect obtained by the three dimensional bulk phonon and by the two dimensional
interface phonon models.
Received 17 September 1998 相似文献
10.
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
11.
X.-J. Fan W.-G. Yin X.-G. Li C.-D. Gong 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):5-10
The dispersion spectrum of single hole in a bilayer composed of plane and chain, each described by t-J model, coupled by - interactions between them, is calculated in terms of self-consistent Born approximation. It was found that for a weak interlayer
coupling the two different quasiparticle bands, plane-like and chain-like bands, show a minimum at (, ) and a maximum at (0, 0) or (, ). In plane-like dispersion we can find an anomalous “flat” region near Fermi surface along the antiferromagnetic Brillouin
zone boundary, which favors the formation of the van-Hove singularities. With increasing interlayer coupling, a large modification
of the dispersions is carried out, the minimum deviates from (, ) and the energy gap of the two bands decreases and finally disappears when the vertical coupling is larger enough. The shapes
of the QP bands are sensitive to the vertical hopping rather than the vertical exchange energy . As the interlayer coupling increases, the shapes of the two QP bands suggest that the chain-like band approaches to that
of quasi-one dimensional model, and the plane-like band undergoes the one layer t - t '-J models' band.
Received 17 March 1999 相似文献
12.
V. Meden J. Fricke C. Wöhler K. Schönhammer 《Zeitschrift für Physik B Condensed Matter》1995,99(1):357-365
We present the exact solution for the time evolution of the electron and phonon momentum distribution for a one-dimensional
polaron model with alinear electronic energy dispersion. The electron momentum distribution is shown to obey aMarkovian quantum kinetic equation. Numerical results for the polaron model are compared to the corresponding exact results, when the
negative momentum states are filled in the initial state. The presence of this Fermi sea modifies the dynamics except in the
short time regime. The different, long time dynamics might show up in comparison of hot electron relaxation of undoped and
doped semiconductors. 相似文献
13.
有不少的极性半导休,电子与表面声学声子和体纵光学声子的耦合弱,但与表面光学声手的耦台强.本文同时考虑体纵光学声子、表面光学声子以及表面声学声予的影响,研究这类半导体的表面电予的性质,采用线性组合算符和拉格朗日乘子法,导出其有效哈密顿量和重正化质量。 相似文献
14.
O. S. Barišić S. Barišić 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):1-9
The translationally invariant diagrammatic quantum perturbation theory (TPT) is applied to the polaron problem on the 1D lattice,
modeled through the Holstein Hamiltonian with the phonon frequency ω0, the electron hopping t and the electron-phonon coupling constant g. The self-energy diagrams of the fourth-order in g are
calculated exactly for an intermittently added electron, in addition to the previously known second-order term. The corresponding
quadratic and quartic corrections to the polaron ground state energy become comparable at t/ω0>1 for g/ω0∼(t/ω0) 1/4 when the electron self-trapping and translation become adiabatic. The corresponding non adiabatic/adiabatic crossover occurs
while the polaron width is large, i.e. the lattice coarsening negligible. This result is extended to the range (t/ω0)1/2>g/ω0>(t/ω0)1/4>1 by considering the scaling properties of the high-order self-energy diagrams. It is shown that the polaron ground state
energy, its width and the effective mass agree with the results found traditionally from the broken symmetry side, kinematic
corrections included. The Landau self-trapping of the electron in the classic self-consistent, localized displacement potential,
the restoration of the translational symmetry by the classic translational Goldstone mode and the quantization of the polaronic
translational coordinate are thus all encompassed by a quantum theory which is translationally invariant from the outset.
This represents the first example, open to various generalizations, of the capability of TPT to hold through the adiabatic
symmetry breaking crossover. Plausible arguments are also given that TPT can describe the g/ω0>(t/ω0)1/2 regime of the small polaron with adiabatic or non-adiabatic translation, i.e., that TPT can cover the whole g/ω0, t/ω0 parameter space of the Holstein Hamiltonian. 相似文献
15.
S. Fratini P. Quémerais 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):99-113
The melting of a Wigner Crystal of electrons placed into a host polar material is examined as a function of the density and
the temperature. When the coupling to the longitudinal optical modes of the host medium is turned on, the WC is progressively
transformed into a polaronic Wigner crystal. We estimate the critical density for crystal melting at zero temperature using
the Lindeman criterion. We show that above a certain critical value of the Fr?hlich electron-phonon coupling, the melting
towards a quantum liquid of polarons is not possible, and the insulator-to-metal transition is driven by the ionization of
the polarons (polaron dissociation). The phase diagram at finite temperature is obtained by making use of the same Lindeman
criterion. Results are also provided in the case of an anisotropic electron band mass, showing that the scenario of polaron
dissociation can be relevant in anisotropic compounds such as the superconducting cuprates at rather moderate e-ph couplings.
Received 13 August 1999 相似文献
16.
The chemical potential μ of a many-body system is valuable since it carries fingerprints of phase changes. Here, we summarize results for μ for a three-dimensional electron liquid in terms of average kinetic and potential energies per particle. The difference between μ and the energy per particle is found to be exactly the electrostatic potential step at the surface. We also present calculations for an integrable one-dimensional many-body system with delta function interactions, exhibiting a BCS-BEC crossover. It is shown that in the BCS regime the chemical potential can be expressed solely in terms of the ground-state energy per particle. A brief discussion is also included of the strong coupling BEC limit. 相似文献
17.
Hsu-Cheng Hsu 《Solid State Communications》2004,131(6):371-375
The coupling strength of the radiative transition of hexagonal ZnO nanowires to the longitudinal optic (LO) phonon polarization field is deduced from temperature dependent photoluminescence spectra. An excitonic polaron formation is discussed to explain why the interaction of free excitons with LO phonons in ZnO nanowires is much stronger than that of bound excitons with LO phonons. The strong exciton-phonon coupling in ZnO nanowires affects not only the Haung-Ray S factor but also the FXA-1LO phonon energy spacing, which can be explained by the excitonic polaron formation. 相似文献
18.
O. S. Barišić S. Barišić 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):1-18
The behavior of the 1D Holstein polaron is described, with emphasis on lattice coarsening effects, by distinguishing between
adiabatic and nonadiabatic contributions to the local correlations and dispersion properties. The original and unifying systematization
of the crossovers between the different polaron behaviors, usually considered in the literature, is obtained in terms of quantum
to classical, weak coupling to strong coupling, adiabatic to nonadiabatic, itinerant to self-trapped polarons and large to
small polarons. It is argued that the relationship between various aspects of polaron states can be specified by five regimes:
the weak-coupling regime, the regime of large adiabatic polarons, the regime of small adiabatic polarons, the regime of small
nonadiabatic (Lang-Firsov) polarons, and the transitory regime of small pinned polarons for which the adiabatic and nonadiabatic
contributions are inextricably mixed in the polaron dispersion properties. The crossovers between these five regimes are positioned
in the parameter space of the Holstein Hamiltonian. 相似文献
19.
C. Honerkamp 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):81-91
We compare the one-loop renormalization group flow to strong coupling of the electronic interactions in the two-dimensional
t-t'-Hubbard model with t' = - 0.3t for band fillings smaller and larger than half-filling. Using a numerical N-patch scheme ( N = 32, ..., 96) we show that in the electron-doped case with decreasing electron density there is a rapid transition from
a d
x2 - y2-wave superconducting regime with small characteristic energy scale to an approximate nesting regime with strong antiferromagnetic
tendencies and higher energy scales. This contrasts with the hole-doped side discussed recently which exhibits a broad parameter
region where the renormalization group flow suggests a truncation of the Fermi surface at the saddle points. We compare the
quasiparticle scattering rates obtained from the renormalization group calculation which further emphasize the differences
between the two cases.
Received 19 December 2000 and Received in final form 28 February 2001 相似文献