共查询到20条相似文献,搜索用时 15 毫秒
1.
O. Filippov K.H. Ringhofer B.I. Sturman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):285-290
Analytically and numerically we investigate the dependence of the first Fourier harmonics of the space-charge field, induced
in an AC-biased sillenite crystal by a light-interference pattern, on the light contrast m. It is shown that within the whole contrast range, 0 < m < 1, these dependences are controlled by the only scalar parameter - the space-charge wave quality factor Q. In the low-contrast limit, m Q
-2, this factor defines the degree of enhancement of the nonlinear response while for larger contrasts it characterizes strong
saturation effects. The data obtained are compared with the results of the previous studies of the AC-response. The possibilities
of experimental detection of predicted dependences and their possible implications are discussed.
Received 13 September 2002 / Received in final form 27 December 2002 Published online 11 February 2003 相似文献
2.
We present an analytical approach of the dynamics of a polymer when it is quenched from a solvent into a good or bad solvent. The dynamics is studied by means of a Langevin equation, first in the absence of hydrodynamic
effect, then taking into account the hydrodynamic interactions with the solvent. The variation of the radius of gyration is
studied as a function of time. In both cases, for the first stage of collapse or swelling, the evolution is described by a
power law with a characteristic time proportional to N
4/3
(N), where N is the number of monomers, without (with) hydrodynamic interactions. At larger times, scaling laws are derived for the diffusive
relaxation time.
Received: 10 March 1998 / Received in final form: 15 September 1998 / Accepted: 25 September 1998 相似文献
3.
H. Rieger R. Juhász F. Iglói 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):409-412
We study random XY and (dimerized) XX spin-1/2 quantum spin chains at their quantum phase transition driven by the anisotropy and dimerization, respectively. Using
exact expressions for magnetization, correlation functions and energy gap, obtained by the free fermion technique, the critical
and off-critical (Griffiths-McCoy) singularities are related to persistence properties of random walks. In this way we determine
exactly the decay exponents for surface and bulk transverse and longitudinal correlations, correlation length exponent and
dynamical exponent.
Received 26 September 1999 相似文献
4.
J. Pierre K. Kaczmarska J. Tobola 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):247-255
The Anderson localisation has been observed in Heusler-type solid solutions where Mn replaces Ti or V in NiTiSb or CoVSb compounds
respectively, due to the atomic and magnetic disorders. The magnetoresistance, Hall effect, thermopower and electron spin
resonance of these solutions are investigated. Strong anomalies appear for the concentration range where a carrier localisation
occurs; the mobility of carriers is strongly reduced, the magnetoresistance scales with the resistivity and the susceptibility
of solid solutions.
Received 31 May 2000 相似文献
5.
M. Leadbeater R.A. Römer M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):643-652
We present calculations of the localisation length, , for two interacting particles (TIP) in a one-dimensional random potential, presenting its dependence on disorder, interaction
strength U and system size. is computed by a decimation method from the decay of the Green function along the diagonal of finite samples. Infinite sample
size estimates are obtained by finite-size scaling. For U=0 we reproduce approximately the well-known dependence of the one-particle localisation length on disorder while for finite
U, we find that with varying between and . We test the validity of various other proposed fit functions and also study the problem of TIP in two different random potentials
corresponding to interacting electron-hole pairs. As a check of our method and data, we also reproduce well-known results
for the two-dimensional Anderson model without interaction.
Received 19 June 1998 and Received in final form 29 October 1998 相似文献
6.
K.M. Frahm 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):371-378
The localization length L2 of two interacting particles in a one-dimensional disordered system is studied for very large system sizes by an efficient
and accurate variant of the Green function method. The numerical results (at the band center) can be well described by the
functional form L
2
=L
1
[0.5+c(U) L
1
] where L1 is the one-particle localization length and the coefficient depends on the strength U of the on-site Hubbard interaction. The Breit-Wigner width or equivalently the (inverse) life time of non-interacting pair
states is analytically calculated for small disorder and taking into account the energy dependence of the one-particle localization
length. This provides a consistent theoretical explanation of the numerically found U-dependence of c(U).
Received 16 September 1998 相似文献
7.
A.N. Lebedev O. Stenzel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(1):83-88
The theory presented by Gerardy
and Ausloos for the calculation of the linear optical response of aggregates of spherical particles is analytically continued for absorbing
embedding media. The method is based on the calculation of the extinction rate by a single particle embedded in an absorbing
matrix. Explicit expressions for the extinction and scattering cross-sections are given. The method is applied to calculate
the energy losses in several organic matrices with embedded silver clusters. Comparison with experimental data shows a very
good agreement.
Received: 21 December 1998 相似文献
8.
A. Kobelkov F. Gleisberg W. Wonneberger 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):21-27
Starting from the static Fukuyama-Lee-Rice equation for a three-dimensional incommensurate charge density wave (CDW) in quasi
one-dimensional conductors a solvable model for local phase pinning by impurities is defined and studied. We find that average
CDW energy and average pinning force show critical behaviour with respect to the pinning parameter h. Specifically the pinning force exhibits a threshold at h=1 with exponent . Our model exemplifies a general concept of local impurity pinning in which the force exerted by the impurity on the periodic
CDW structure becomes multivalued and metastable states appear beyond a threshold. It is found that local impurity pinning
becomes less effective at low temperatures and may eventually cease completely. These results are independent of spatial dimensionality
as expected for local impurity pinning. Comparison with Larkin's model is also made.
Received 8 July 1998 相似文献
9.
E. Cormier M. Lewenstein 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(2):227-233
We address the problem of the optimization of high-order harmonic generation by two laser fields of frequencies and respectively, through a theoretical approach. The parameters that are investigated are the two lasers intensities as well
as the relative phase between the two fields. We show that a moderate, but significant increase of efficiency can be achieved
in that context and give the domain of optimized parameters. Moreover, we quantitatively investigate the gain and set the
limitation of the optimization using such coherent control methods.
Received 3 March 2000 and Received in final form 4 May 2000 相似文献
10.
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
11.
12.
F. Bassani V. Lucarini 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):567-573
We use the Kubo response function formalism to derive the asymptotic behaviour of the harmonic generation susceptibilities
to all orders n. The results show a stringent correspondence with the ones previously obtained from the classical anharmonic oscillator model.
They are characterized by a dependence and a coefficient proportional to the trace of the (n+1)th derivative of the potential energy on the equilibrium density matrix. Using the above results we derive new Kramers-Kr?nig
relations and sum rules for all orders of harmonics susceptibilities.
Received 17 April 2000 相似文献
13.
T. Schaub J. Delahaye C. Berger H. Guyot R. Belkhou A. Taleb-Ibrahimi Y. Calvayrac 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):183-188
High resolution photoemission measurements performed at low temperatures on a single-grained sample of the AlPdMn icosahedral
phase show that the density of states N(E) strongly depends on the nature of the surface. For an ordered quasicrystalline surface, prepared by Ar etching and ultra
high vacuum annealing, a dip feature is observed in N(E) near the Fermi level, which energy dependence can be analyzed with a simple square-root power law. By contrast, N(E) varies only little with energy both for a disordered surface and a crystalline surface of the same sample. A sharp Fermi
edge is then clearly observed. This shows that the metallic character of the surface of a quasicrystal is strongly reduced
when the surface presents a quasicrystalline ordering.
Received 19 February 2000 and Received in final form 6 November 2000 相似文献
14.
R. Citro M. Marinaro 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):235-242
The spin magnetic susceptibility of the p-d model is calculated by means of a perturbation theory in the hybridization term V through a generalized cumulant expansion (GCE). The analysis is approached from the paramagnetic metallic phase. The results
qualitatively reproduce some unusual magnetic properties in the normal state of the hole-doped cuprates, supporting the scenario
of a Van Hove singularity near the Fermi level.
Received 15 October 1998 and Received in final form 24 March 1999 相似文献
15.
M.S. Mikhelashvili 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):187-192
A common theory of reversible charge transfer (RCT) kinetics for low and high excitation power with the use of the conditional
concentration of acceptors is presented. A comparison with recently published RCT theory is given. The results are similar
or identical only in restricted or fractal spaces of low dimension, and in the case of low concentration of acceptors, i.e. in all the cases when the conditions of the binary approximation are fulfilled. The deviation from the binary approximation
results in a physically incorrect picture, the cause being due to the different space averaging procedure. The probability
of the donor's cation state is an increasing function of the concentration of the acceptor and of the characteristic parameters
of the rate constants.
Received 26 May 1999 相似文献
16.
E. Farhi A.K. Tagantsev R. Currat B. Hehlen E. Courtens L.A. Boatner 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):615-623
High resolution data on low energy phonon branches (acoustic and soft optic) along the three principal symmetry axes in pure
KTaO3 were obtained by cold neutron inelastic scattering between 10 and 80 K. Additional off-principal axis measurements were performed
to characterize the dispersion anisotropy (away from the and axes). The parameters of the phenomenological model proposed by Vaks [28] are refined in order to successfully describe the
experimental low temperature (10 <
T
< 100 K) dispersion curves, over an appreciable reciprocal space volume around the zone center ( rlu). The refined model, which involves only 4 temperature-independent adjustable parameters, is intended to serve as a basis
for quantitative computations of multiphonon processes.
Received: 29 September 1999 and Received in final form 6 January 2000 相似文献
17.
Ll. Serra A. Puente 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):77-81
The magnetic extension of the Thomas-Fermi-Weizs?cker kinetic energy is used within density-functional-theory to numerically
obtain the ground state densities and energies of two-dimensional quantum dots. The results are thoroughly compared with the
microscopic Kohn-Sham ones in order to assess the validity of the semiclassical method. Circular as well as deformed systems
are considered.
Received 26 October 2000 and Received in final form 14 December 2000 相似文献
18.
D. Basko G.C. La Rocca F. Bassani V.M. Agranovich 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):353-362
We predict an efficient electronic energy transfer from an excited semiconductor quantum well to optically active organic
molecules of the nearby medium (substrate and/or overlayer). The energy transfer mechanism is of the F?rster type and, at
semiconductor-organic distances of about 50 ?, can easily be as fast as 10-100 ps, which is about an order of magnitude shorter
than the effective exciton lifetime in an isolated quantum well. In such conditions, the Wannier-Mott exciton luminescence
is quenched and the organic luminescence is efficiently turned on. We consider both free as well as localized quantum well
excitons discussing the dependence of the energy transfer rate on temperature and localization length. A similar mechanism
for the non-radiative energy transfer to the organic overlayer molecules from unbound electron-hole pairs excited in the 2D
continuum is shown to be much less competitive with respect to other relaxation channels inside the inorganic quantum well
(in particular, 2D exciton formation).
Received 20 July 1998 相似文献
19.
20.
R. Monasson 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):555-567
The spectral properties of the Laplacian operator on “small-world” lattices, that is mixtures of unidimensional chains and
random graphs structures are investigated numerically and analytically. A transfer matrix formalism including a self-consistent
potential à la Edwards is introduced. In the extended region of the spectrum, an effective medium calculation provides the density of states
and pseudo relations of dispersion for the eigenmodes in close agreement with the simulations. Localization effects, which
are due to connectivity fluctuations of the sites are shown to be quantitatively described by the single defect approximation
recently introduced for random graphs.
Received 23 March 1999 相似文献