共查询到20条相似文献,搜索用时 15 毫秒
1.
M. Dressler F. Bassani G. Czajkowski 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):681-686
We show how to compute the optical functions (reflectivity, transmission, and absorption) of polydiacetylene chains diluted
in their monomer matrix exposed to a uniform electric field in the chain direction, in the excitonic energy region. Adopting
a model electron-hole potential, we derived an analytical expression for the effective chain susceptibility, which gives the
optical functions. The resulting absorption shows excitonic peaks below the gap and Franz-Keldysh oscillations above the gap.
The method has been applied for a 3BCMU polydiacetylene chain, showing a good agreement with experimental spectra.
Received 5 November 1998 and
Received in final form 23 February 1999 相似文献
2.
The negatively charged exciton in double-layer quantum dots 总被引:1,自引:0,他引:1
Wenfang Xie 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):385-389
The hyperangular equation for charged semiconductor complexes in a double-layer harmonic quantum dot was solved numerically
by using the correlated hyperspherical harmonics as basis functions. By using this method, we have calculated the energy spectra
of the low-lying states of a charged exciton as a function of the radius of the quantum dot and the binding energy spectra
of the ground state as a function of the radius of the quantum dot for a few values of the distance between the vertically
coupled dots and the electron-to-hole mass ratio.
Received 3 December 1999 相似文献
3.
J.J. Liu S.F. Zhang Y.X. Li X.J. Kong 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):17-20
Using a two-parameter wave function, we calculate variationally the binding energy of an exciton bound to an ionized donor
impurity (D+,X) in GaAs-AlxGa1-xAs quantum wells for the values of the well width from 10 to 300 ?, when the dopant is located in the center of the well and
at the edge of the well. The theoretical results confirm that the previous experimental speculation proposed by Reynolds et al. [Phys. Rev. B 40, 6210 (1989)] is the binding energy of D+,X for the dopant at the edge of the well. In addition, we also calculate the center-of-mass wave function of the exciton and
the average interparticle distances. The results are discussed in detail.
Received 17 July 2000 and Received in final form 13 November 2000 相似文献
4.
J. Bellessa V. Voliotis T. Guillet D. Roditchev R. Grousson X.L. Wang M. Ogura 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):499-505
We report on time-resolved microphotoluminescence experiments in a single GaAs/GaAlAs V-shaped quantum wire as a function
of optical excitation intensity. At low pump power we observe that excitons are localized in quantum boxes formed by the local
potential minima existing along the wire axis. As the pump power is increased, state filling of the lowest lying levels of
the boxes appears. When two carriers occupy the first excited level of the box, a very efficient Auger scattering occurs,
leading to a transfer of carriers from one box to another neighbouring one. The intradot Auger scattering time has been measured
and is of the same order of magnitude as the LA-phonon emission rate.
Received 5 February 2001 相似文献
5.
C. Sieh T. Meier A. Knorr F. Jahnke P. Thomas S. W. Koch 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):407-421
A model study of the characteristic signatures of carrier-correlation effects on the excitonic differential absorption spectra
in semiconductors is presented. Using an effectively one-dimensional tight-binding system Coulomb-induced carrier-correlations
up to third-order in the optical field are treated without additional approximations. To illustrate the influence of the different
many-body contributions excitonic differential absorption spectra are computed for various polarizations and pump-probe time
delays. The simultaneous influence of energetic disorder and correlations on the differential absorption spectra is discussed.
Also presented are numerical results for the case when the semiconductor system is placed inside a microcavity in the strong-coupling
regime. It is shown that the correlations induce characteristic signatures in the normal mode spectra.
Received 22 January 1999 相似文献
6.
M. Geddo R. Ferrini G. Guizzetti M. Patrini S. Franchi P. Frigeri G. Salviati L. Lazzarini 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):19-24
We report on a photoreflectance investigation in the 0.8-1.5 eV photon energy range and at temperatures from 80 to 300 K on
stacked layers of InAs/GaAs self-assembled quantum dots (QDs) grown by Atomic-Layer Molecular Beam Epitaxy. We observed clear
and well-resolved structures, which we attribute to the optical response of different QD families. The dependence of the ground
state transition energy on the number of stacked QD layers is investigated and discussed considering vertical coupling between
dots of the same column. It is shown that Coulomb interaction can account for the observed optical response of QD families
with different morphology coexisting in the same sample.
Received 17 November 1999 相似文献
7.
We reconsider the semiconductor trions from scratch. We first determine the very many “reasonable” ways to write the trions
in first quantization. We then select the forms which are easy to relate to physical pictures. In a second part, we derive
the corresponding creation operators in second quantization. We pay particular attention to the expression of the X- trion in terms of exciton and free-electron, as it is the one adapted to future works on many-body effects with trions.
Received 27 May 2002 / Received in final form 18 December 2002 Published online 20 June 2003
RID="a"
ID="a"e-mail: combescot@gps.jussieu.fr 相似文献
8.
Z. P. Wang X. X. Liang X. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):41-46
Polaron effects on excitons in parabolic quantum wells are
studied theoretically by using a variational approach with the so-called
fractional dimension model. The numerical results for the exciton binding
energies and longitudinal-optical phonon contributions in
GaAs/Al0.3Ga0.7As parabolic quantum well structures are obtained as functions of the well width. It is shown that the exciton binding energies
are obviously reduced by the electron (hole)-phonon interaction and the polaron effects are un-negligible. The results demonstrate
that the fractional-dimension variational theory is effectual in the investigations of excitonic polaron problems in parabolic
quantum wells. 相似文献
9.
O.M. Schmitt D.B. Tran Thoai P. Gartner H. Haug 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):217-222
The dephasing and relaxation kinetics of bosonic excitons interacting with a thermal bath of acoustic phonons is studied after
coherent pulse excitation. The kinetics of the induced excitonic polarization is calculated within Markovian equations both
for subcritical and supercritical excitation with respect to a Bose-Einstein condensation (BEC). For excited densities n below the critical density , an exponential polarization decay is obtained, which is characterized by a dephasing rate . This dephasing rate due to phonon scattering shows a pronounced exciton-density dependence in the vicinity of the phase
transition. It is well described by the power law that can be understood by linearization of the equations around the equilibrium solution. Above the critical density we get
a non-exponential relaxation to the final condensate value p0 with that holds for all densities. Furthermore we include the full self-consistent Hartree-Fock-Bogoliubov (HFB) terms due to
the exciton-exciton interaction and the kinetics of the anomalous functions . The collision terms are analyzed and an approximation is used which is consistent with the existence of BEC. The inclusion
of the coherent exciton-exciton interaction does not change the dephasing laws. The anomalous function Fk exhibits a clear threshold behaviour at the critical density.
Received 13 December 1999 相似文献
10.
D. Brinkmann J.E. Golub S.W. Koch P. Thomas K. Maschke I. Varga 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):145-148
A two-band model of a disordered semiconductor is used to analyze dynamical interaction induced weakening of localization
in a system that is accessible to experimental verification. The results show a dependence on the sign of the two-particle
interaction and on the optical excitation energy of the Coulomb-correlated electron-hole pair.
Received 4 September and Received in final form 26 November 1998 相似文献
11.
W. Ouerghui J. Martinez-Pastor J. Gomis M. A. Maaref D. Granados J. M. García 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):217-223
Exciton recombination dynamics in vertical stacks of InGaAs quantum rings have been studied by means of continuous wave and
time resolved
photoluminescence under low excitation density conditions. We have paid
special attention to the effect of the carrier coupling on the exciton
radiative lifetime: weak (14 nm spacer sample), intermediate (4.5 nm spacer
sample), where the size filtering effects (towards small rings) compensate
partially that arising from carrier coupling (towards lower energies), and
strong electron and hole coupling (1.5 nm spacer sample) between layers.
Experimental decay times in the latter two cases have been compared to the
times simulated with a multi-quantum well based model, which accounts for
the observed change of carrier coupling regime. The most important effect is
observed when the hole wave function overlap along the growth direction
becomes important (1.5 nm spacer sample). This situation makes important the
lateral tunneling of excitons between rings, given their large lateral size,
which is characterized by times around 5 ns at the emission peak energy
(rings with the most probable size of the distribution). 相似文献
12.
G. H. Fecher J. Braun N. A. Cherepkov L. V. Chernysheva Th. Jentzsch J. Morais A. Oelsner Ch. Ostertag J. Paul H. Ufer G. Schönhense 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):161-175
We present investigations of the electronic and magnetic structure of the Rare Earth valence states. In particular, we have
examined ultra thin films of the rare earth metals gadolinium and neodymium epitaxially grown on tungsten (110). Various experiments on dichroism in
angular resolved photoemission have been performed using circularly as well as linearly polarised light in the VUV-range with
photon energies below 40 eV. A special emphasis was placed on the investigation of the surface state, which was observed for both Gd and Nd. A
very small magnetic splitting of about 25 meV was observed for the surface state of ferromagnetic Gd. A magnetic ordering
of a Nd-monolayer on a remanently magnetised Fe-film is observed. Large dichroism effects are found for the surface state
as well as the valence bands of paramagnetic Nd. In the latter case, these are used to determine the dispersion of the valence
bands. Different numerical approaches are presented, one based on atomic photoionisation theory, another is based on a one-step
model of solid state photoemission. Atomic photoionisation theory is used together with three-step calculations to explain
the non-magnetic circular dichroism observed in the Gd 4f emission. The capability of dichroism experiments for resolving details of the electronic structure and for sensitive tests
of photoemission calculations is demonstrated.
Received 21 September 1998 相似文献
13.
14.
X.-F. Zhao C.-H. Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(2):209-212
Electron Raman scattering (ERS) is investigated in a
free-standing semiconductor quantum wire of cylindrical geometry for
two classes of materials CdS and GaAs. The differential cross
section (DCS) involved in this process is calculated as a function
of a scattering frequency and the radius of the cylinder. Electron
states are considered to be confined within a free-standing quantum
wire (FSW). Single parabolic conduction and valence bands are
assumed. The selection rules are studied. Singularities in the
spectra are found and interpreted for various radii of the cylinder. 相似文献
15.
I. Milosević T. Vuković M. Damnjanović B. Nikolić 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):707-712
The full geometrical symmetry groups (the line groups) of the monolayered, 2Hb and 3R polytypes of the inorganic MoS2 and WS2 micro- and nanotubes of arbitrary chirality are found. This is used to find the coordinates of the representative atoms sufficient
to determine completely the geometrical structure of the tubes. Then some physical properties which can be deduced from the
symmetry are discussed: electron band degeneracies, selection rules, general forms of the second rank tensors and potentials,
phonon spectra.
Received 13 April 2000 相似文献
16.
Q. Guo Y.P. Feng H.C. Poon C.K. Ong 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):29-36
A new approach based on the invariant embedding method for the self-consistent calculation of electronic structure of quantum
wells is presented and is applied to both neutral quantum well and parabolic quantum well. Numerical results obtained for
these structures agree very well with those of previous theoretical and experiment studies. The present approach is expected
to lead to a more efficient and stable scheme for the calculation of electronic band structure of quantum structures. Realistic
boundary conditions are naturally taken into account in the present calculation which provides a convenient way for studying
boundary effects.
Received 21 September 相似文献
17.
W. Pogosov M. Combescot 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(2):183-192
By using the composite many-body theory for Frenkel excitons we have recently developed, we here derive the ground state energy
of N Frenkel excitons in the Born approximation through the Hamiltonian mean value in a state made of N identical Q = 0 excitons. While this quantity reads as a density expansion in the case of Wannier excitons, due to many-body effects induced
by fermion exchanges between N composite particles, we show that the Hamiltonian mean value for N Frenkel excitons only contains
a first order term in density, just as for elementary bosons. Such a simple result comes from a subtle balance, difficult
to guess a priori, between fermion exchanges for two or more Frenkel excitons appearing in Coulomb term and the ones appearing
in the N exciton normalization factor – the cancellation being exact within terms in 1/Ns where Ns is the number of atomic sites in the sample. This result could make us naively believe that, due to the tight binding approximation
on which Frenkel excitons are based, these excitons are just bare elementary bosons while their composite nature definitely
appears at various stages in the precise calculation of the Hamiltonian mean value. 相似文献
18.
Z. Barticevic M. Pacheco C. A. Duque L. E. Oliveira 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(4):303-309
A theoretical study, within the effective-mass approximation, of the
effects of applied magnetic fields on excitons in disk-shaped
GaAs-Ga1-xAlxAs quantum dots is presented. Magnetic fields
are applied in the growth direction of the semiconductor
heterostructure. The parity of the excitonic envelope function
related to the simultaneous exchange of ze→-ze and
zh→-zh is a good quantum number and the wave
function, both the odd and even parity, can be expanded as
combination of products of the quantum well electron and hole
function that preserves the parity with appropriate Gaussian
functions. We have simultaneously obtained the energies of the
excitonic ground and excited states and discuss the behavior of
these energies as a function of the magnetic field. 相似文献
19.
O.A. Yeshchenko M.M. Biliy Z.Z. Yanchuk 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):37-43
Excitonic absorption, reflection and photoluminescence spectra of mixed Zn(P1-xAsx)2 crystals over the full range of x ( 0 ?
x
? 1) and Zn1-xCdxP2 crystals at 0 ?
x
? 0.05 have been studied at low temperatures (1.8 K). The decrease of the energy gap in Zn(P1-xAsx)2 at the increase of x occurs slightly sublinearly. The rydbergs of excitonic series in this crystals decrease as well, and the dependences Ry
(
x
) for all series are strongly superlinear at small x. In Zn1-xCdxP2 crystals the energy gap and rydbergs decrease at the increase of x (at 0 ?
x
? 0.05) as well. The dependences of Eg and Ry on x are considerably stronger in Zn(P1-xAsx)2 than in Zn1-xCdxP2. At the increase of x the half-width of excitonic absorption lines increases monotonically in both type crystals that is evidence of the increasing
role of fluctuations of crystal potential.
Received 13 March 2002 Published online 9 July 2002 相似文献
20.
R. Schuster M. Knupfer D. R.T. Zahn H. Berger 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):25-28
We have investigated the polarization and momentum
dependence of singlet excitons in pentacene molecular crystals
using inelastic electron scattering. Our results demonstrate that
both the direction as well as the absolute value of the momentum
are decisive for the spectral intensity of these excitons.
Possible implications of this observation for a microscopic
understanding of excitons in organic molecular crystals are
discussed. 相似文献