共查询到20条相似文献,搜索用时 31 毫秒
1.
Z. An B. Di H. Zhao C. Q. Wu 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(1):71-77
Within an one-dimensional tight-binding model, we
investigate the inelastic scattering processes of oppositely
charged polarons in conjugated polymers under the influence of an
external electric field, by using a nonadiabatic evolution method.
It is found that the polaron pair does not necessarily scatter
into an entity(neutral exciton), but a mixed state composed of
both polarons and excitons. The yield of the neutral exciton
depends sensitively on the strength of applied fields.
Additionally, effects of interchain coupling on the scattering
processes are also discussed, which shows that the interchain
coupling is of fundamental importance and facilitates the
formation of the polaron-exciton. 相似文献
2.
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
3.
4.
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
5.
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
6.
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
7.
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
8.
J. Loos 《Zeitschrift für Physik B Condensed Matter》1994,96(2):149-158
The coupling between the charge transfer and the lattice fluctuations is proposed as a possible mechanism of the superconductivity in the polaron system near the cross-over from the quasi-localized to the delocalized regime. The corresponding self-energy matrix is deduced using the Holstein Hamiltonian and the equations for the off-diagonal order are formulated. The lower bound on the superconducting critical temperature is estimated and the possible relevance of the proposed mechanism for the superconducting copper oxides is discussed. 相似文献
9.
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
10.
Due to solvation, excess charge carriers on 1d semiconductor nanostructures immersed in polar solvents undergo self-localization into polaronic states. Using a simplified theoretical model for small-diameter structures, we study low-frequency dynamical properties of resulting 1d adiabatic polarons. The combined microscopic dynamics of the electronic charge density and the solvent leads to macroscopic Langevin dynamics of a polaron and to the appearance of local dielectric relaxation modes. Polaron mobility is evaluated as a function of system parameters. Numerical estimates indicate that the solvated carriers can have mobilities orders of magnitude lower than the intrinsic values. 相似文献
11.
H. Barentzen 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):197-209
An analytic study is presented of the E⊗e Jahn-Teller (JT) polaron, consisting of a mobile eg electron linearly coupled to the local eg normal vibrations of a periodic array of octahedral complexes. Due to the linear coupling, the parity operator and the angular momentum operator commute with the JT part and cause a twofold degeneracy of each JT eigenvalue. This degeneracy is lifted by the anisotropic
hopping term. The Hamiltonian is then mapped onto a new Hilbert space, which is isomorphic to an eigenspace of belonging to a fixed angular momentum eigenvalue j > 0. In this representation, the Hamiltonian depends explicitly on j and decomposes into a Holstein term and a residual JT interaction. While the ground state of the JT polaron is shown to belong
to the sector j = 1/2, the Holstein polaron is obtained for the “unphysical” value j = 0. The new Hamiltonian is then subjected to a variational treatment, yielding the dispersion relations and effective masses
for both kinds of polarons. The calculated polaron masses are in remarkably good agreement with recent quantum Monte Carlo
data. The possible relevance of our results to the magnetoresistive manganite perovskites is briefly discussed.
Received 6 July 2001 相似文献
12.
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
13.
Dalibor ?evizovi? Slobodanka Galovi? Slobodan Zekovi? Zoran Ivi? 《Physica B: Condensed Matter》2009,404(2):270-274
The transition from band to hopping conductivity of small polaron is examined within Holstein's molecular crystal model. The conditions under which each of these mechanisms prevail are formulated in terms of the values of the coupling constant S and adiabatic parameter B. Particular attention was paid to the possible influence of the polaron induced modification of phonon spectrum. 相似文献
14.
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
15.
Bakhrom Yavidov 《Physica B: Condensed Matter》2009,404(20):3756-3760
In this work renormalization of the effective mass of an electron due to a small polaron formation is studied within the framework of the extended Holstein model. It is assumed that an electron moves along the one-dimensional chain of ions and interacts with ions vibrations of a neighboring chain via a long-range density-displacement type force. By means of the exact calculations a renormalized mass of a nonadiabatic small polaron is obtained at strong coupling limit. The obtained results compared with the mass of small polaron of ordinary Holstein model. The effect of ions vibrations polarization on the small polaron mass is addressed. 相似文献
16.
Relaxation process of self-trapped polaron is investigated by a nonadiabatic molecular dynamic method. We show localized disorder due to lattice fluctuations can give rise to a tightly-bound electronic state in ultraviolet illuminated SrTiO3 crystal. This bound state is actually a self-trapped polaron in accordance with the experimentally observed large Stokes-shift. The formation of the self-trapped polaron is shown to be an ultrafast process. 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.
We present a unified view of the transport properties of small polarons in the Holstein model at low carrier densities, based on the dynamical mean-field theory. The nonperturbative nature of the approach allows us to study the crossover from classical activated motion at high temperatures to coherent motion at low temperatures. Large quantitative discrepancies from the standard polaronic formulas are found. The scaling properties of the resistivity are analyzed, and a simple interpolation formula is proposed in the nonadiabatic regime. 相似文献
19.
THE PROPERTIES OF THE GROUND STATE OF THE NONADIABATICALLY COUPLED ELECTRON-PHONON SYSTEMS WITH CORRELATED DISPLACEMENT AND SQUEEZING 下载免费PDF全文
Eeffcts of the nonadiabatic phonon fluctuations on the ground state of coupled onedimensional electron-phonon systems with high and low electron-densities were investigated by a new ansatz including correlated interaction of the displacement and squeezing. The correlated effect resulted in noticeable reduction of ground state energy of the systems, and obvious increases of binding energy of the polarons occurred. Thus,the stabilities of the polaron and of the systems were significantly enhanced,exactly steady ground state of the Holstein model, then,was obtained by the new ansatz for the coupled electron-phonon systems. In general,the new ansatz were found to be very relevant for the strong coupling and large squeezing cases in nonadiabatically coupled electron-photon systems. 相似文献
20.
Renormalization of the mass of an electron is studied within the framework of the Extended Holstein model at strong coupling regime and nonadiabatic limit. In order to take into account an effect of screening of an electron-phonon interaction on a polaron it is assumed that the electron-phonon interaction potential has the Yukawa form and screening of the electron-phonon interaction is due to the presence of other electrons in a lattice. The forces are derived from the Yukawa type electron-phonon interaction potential. It is emphasized that the early considered screened force of (Kornilovitch (1998), Spencer et al. (2005), Hague et al. (2006), Hague and Kornilovitch (2009)) Refs. [7], [18], [19] and [22] is a particular case of the force deduced from the Yukawa potential and is approximately valid at large screening radiuses compared to the distances under consideration. The Extended Holstein polaron with the Yukawa type potential is found to be a more mobile than polaron studied in early works at the same screening regime. 相似文献