共查询到20条相似文献,搜索用时 31 毫秒
1.
S. Fratini P. Quémerais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):41-49
We consider a three dimensional Wigner crystal of electrons lying in a host ionic dielectric. Owing to their interaction with
the lattice polarization, each localized electron forms a polaron. We study the collective excitations of such a polaronic
Wigner crystal at zero temperature, taking into account the quantum fluctuations of the polarization within the Feynman harmonic
approximation. We show that, contrary to the ordinary electron crystal, the system undergoes a polarization catastrophe when
the density is increased. An optical signature of this instability is derived, whose trend agrees with the experiments carried
out in Nd-based cuprates.
Received 4 July 2002 Published online 17 September 2002 相似文献
2.
J. Tempere S.N. Klimin I.F. Silvera J.T. Devreese 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):329-338
The properties of ripplonic polarons in a multielectron bubble in liquid helium are investigated on the basis of a path-integral
variational method. We find that the two-dimensional electron gas can form deep dimples in the helium surface, or ripplopolarons,
to solidify as a Wigner crystal. We derive the experimental conditions of temperature, pressure and number of electrons in
the bubble for this phase to be realized. This predicted state is distinct from the usual Wigner lattice of electrons: it
melts by dissociation of the ripplopolarons when the electrons shed their localizing dimple as the pressure on the multielectron
bubble drops below a critical value.
Received 20 February 2003 Published online 11 April 2003
RID="a"
ID="a"Also at: TU Eindhoven, Eindhoven, The Netherlands e-mail: devreese@uia.ua.ac.be 相似文献
3.
Serghei N. Klimin Jacques Tempere Vyacheslav R. Misko Michiel Wouters 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(8):172
Electrons on liquid helium can form different phases depending on density, and temperature. Also the electron-ripplon coupling strength influences the phase diagram, through the formation of so-called “ripplonic polarons”, that change how electrons are localized, and that shifts the transition between the Wigner solid and the liquid phase. We use an all-coupling, finite-temperature variational method to study the formation of a ripplopolaron Wigner solid on a liquid helium film for different regimes of the electron-ripplon coupling strength. In addition to the three known phases of the ripplopolaron system (electron Wigner solid, polaron Wigner solid, and electron fluid), we define and identify a fourth distinct phase, the ripplopolaron liquid. We analyse the transitions between these four phases and calculate the corresponding phase diagrams. This reveals a reentrant melting of the electron solid as a function of temperature. The calculated regions of existence of the Wigner solid are in agreement with recent experimental data. 相似文献
4.
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
5.
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
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.
J. R. Iglesias R. M. C. de Almeida 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(3):1-10
Large adiabatic polarons in anisotropic crystals in the presence of constant magnetic field have been studied within the Holstein molecular crystal model in the continuum approximation. It was shown that magnetic field directed along the symmetry axis induces transverse confinement which may stabilize large polarons. They represent localized (soliton-like) nonlinear structure uniformly propagating along the symmetry axis and rotating around it in the same time. Such objects exist in 3D lattice provided that coupling constant and magnetic field do not exceed certain critical values. In contrast with pure 1D systems existence of large polarons is possible in a quite wider region of the values of coupling constant which may attain considerably higher values than in the pure 1D media. Furthermore, polaron effective mass, depending on the intensity of the applied magnetic field, may be considerably lighter than that of the the pure 1D polarons for the same values of coupling constant. This is the most significant difference with respect to pure 1D systems in the absence of magnetic field and may have substantial impact on polaron transport properties. 相似文献
8.
J. C. Li J. Zhu Z. J. Peng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):325-330
We study analytically and numerically the properties of one-dimensional
chain of cold ions placed in a periodic potential of optical lattice
and global harmonic potential of a trap.
In close similarity with the Frenkel-Kontorova model, a transition from
sliding to pinned phase takes place with the increase of
the optical lattice potential for the density of ions
incommensurate with the lattice period. We show that at zero temperature the quantum
fluctuations lead to a quantum phase transition
and melting of pinned instanton glass phase at large values of dimensional Planck constant.
After melting the ion chain can slide in an optical lattice.
The obtained results are also relevant for a Wigner crystal placed
in a periodic potential. 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.
L. Turban 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):273-285
We study the influence of an aperiodic extended surface perturbation on the surface critical behaviour of the two-dimensional
Ising model in the extreme anisotropic limit. The perturbation decays as a power of the distance l from the free surface with an oscillating amplitude where follows some aperiodic sequence with an asymptotic density equal to 1/2 so that the mean amplitude vanishes. The relevance
of the perturbation is discussed by combining scaling arguments of Cordery and Burkhardt for the Hilhorst-van Leeuwen model
and Luck for aperiodic perturbations. The relevance-irrelevance criterion involves the decay exponent , the wandering exponent which governs the fluctuation of the sequence and the bulk correlation length exponent . Analytical results are obtained for the surface magnetization which displays a rich variety of critical behaviours in the
-plane. The results are checked through a numerical finite-size-scaling study. They show that second-order effects must be
taken into account in the discussion of the relevance-irrelevance criterion. The scaling behaviours of the first gap and the
surface energy are also discussed.
Received 1 December 1998 相似文献
11.
X. L. Yu S. L. Ban 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):483-491
The Larsen perturbation method is adopted to study the
influence of magnetic fields on polarons in realistic heterojunctions in a
quasi-two-dimension approximation. The interaction between an electron and
both the bulk longitudinal optical phonons and the two branches of interface
optical phonons is taken into account to show the influence of magnetic
fields at different ranges on the polaron cyclotron mass due to the coupling
of the electron with each branch of phonon modes. The result indicates that
not only do the bulk phonons influence the polaron cyclotron mass, but the
interface phonons do as well. The pressure effect on the cyclotron mass is
also discussed. 相似文献
12.
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
13.
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
14.
L. Proville S. Aubry 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):405-421
We study the effective mass of the bipolarons and essentially the possibility to get both light and strongly bound bipolarons
in the Holstein-Hubbard model and some variations in the vicinity of the adiabatic limit. Several approaches to investigate
the quantum mobility of polarons and bipolarons are proposed for this model. First, the quantum fluctuations are treated as
perturbations of the mean-field (or adiabatic) approximation of the electron-phonon coupling in order to calculate the bipolaron
bands. It is found that the bipolaron mass generally remains very large except in the vicinity of the triple point of the
phase diagram (see [1]), where the bipolarons have several degenerate configurations at the adiabatic limit (single site (S0),
two sites (S1) and quadrisinglet (QS)), while the polarons are much lighter. This degeneracy reduces the bipolaron mass significantly.
Next we improve this result by variational methods (modified Toyozawa Exponential Ansatz or TEA) valid for larger quantum
perturbations away from the adiabatic limit. We first test this new method for the single polaron. We find that the triple
point of the phase diagram is washed out by the lattice quantum fluctuations which thus suppress the light bipolarons. Further
improvements of the method by hybridization of several TEA states do not change this conclusion. Next we show that some model
variations, for example a phonon dispersion may increase the stability of the (QS) bipolaron against the quantum lattice fluctuations.
We show that the triple point of the phase diagram may be stable to quantum lattice fluctuations and a very sharp mass reduction
may occur, leading to bipolaron masses of the order of 100 bare electronic mass for realistic parameters. Thus we argue that
such very light bipolarons could condense as a superconducting state at relatively high temperature when their interactions
are not too large, that is, their density is small enough. This effect might be relevant for understanding the origin of the
high superconductivity of doped cuprates far enough from half filling.
Received 15 September 1999 相似文献
15.
The ground-state energy and effective mass of an acoustic polaron in one dimension are calculated by using an electron-longitudinal-acoustic-phonon interaction Hamiltonian derived here. The self-trapping of the acoustic polaron is discussed. It is found that the critical coupling constant shifts toward weaker electron-phonon interaction with the increasing cutoff wave vector and the products of the critical coupling constant by the cutoff wave vector tend to a certain value. The self-trapping of acoustic polarons in one dimension is easier to be realized than that in three- and two-dimensional systems. The self-trapping transition of acoustic polarons is expected to be observed in the one dimensional systems of alkali halides and wide-band-gap semiconductors. 相似文献
16.
G.N. Katomeris S.N. Evangelou 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):133-136
We examine the validity of the recently proposed semi-Poisson level spacing distribution function P(S), which characterizes “critical quantum chaos”, in 2D disordered systems with spin-orbit coupling. At the Anderson transition
we show that the semi-Poisson P(S) can describe closely the critical distribution obtained with averaged boundary conditions, over Dirichlet in one direction
with periodic in the other and Dirichlet in both directions. We also obtain a sub-Poisson linear number variance , with asymptotic value . The obtained critical statistics, intermediate between Wigner and Poisson, is discussed for disordered systems and chaotic
models.
Received 1 September 1999 相似文献
17.
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
18.
二维声学极化子的基态能量和有效质量 总被引:1,自引:1,他引:0
自陷电子对了解光电材料的光学性质非常重要.近些年来,形变晶格中电子自陷的问题受到研究人员的广泛关注.电子既与声学模耦合,也与光学模相互作用,但电子由自由态向自陷态的转变缘于近程的电子-声学声子耦合.研究表明:声学极化子在大多数半导体以及Ⅲ-Ⅴ族化合物,甚至碱卤化物中都不可能自陷.另一方面,电子-声子耦合在束缚结构,如二维、一维系统中,会有所增强.换言之,电子在低维结构中更容易自陷.Farias等人指出:声学极化子在二维系统中自陷的临界电子-声子耦合常数为定值,不随声子截止波矢的变化而改变.这种结论在物理上不尽合理.通过计算二维系统中的声学极化子基态能量和有效质量,讨论了二维声学极化子自陷问题.研究发现,二维声学极化子自陷转变的临界耦合常数随声子截止波矢的增加朝电子-声子耦合较弱的方向变化.这一特征与前人关于体和表面极化子研究获得的结论定性一致.所得二维声学极化子基态能量的表达式与Farias等人一致,但自陷的结果与Farias等人的结果在定性和定量上均有不同,我们认为Farias等人关于二维声学极化子自陷转变点的确定方式有不妥之处.通过改进自陷转变点的确定方式,得到了在物理上更合理的结果. 相似文献
19.
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
20.
《Physics letters. A》2019,383(33):125954
We report the effects of electron-phonon coupling on the charge density distribution of polarons in armchair nanoribbons of silicene by using an extended tight-binding model with lattice relaxation. The results show that the charge distribution in silicene nanoribbons is analogous to graphene and that the charge localization increases when the intensity of electron-phonon coupling also increases. We further show that silicene nanoribbons may be a conducting or semiconducting material, depending on both the width of the nanoribbon and the possibility of polaron formation. This contribution provides additional insight into the behavior of polarons in silicene nanoribbons, systems of great interest. 相似文献