共查询到20条相似文献,搜索用时 15 毫秒
1.
M. Belhadi O. Rafil R. Tigrine A. Khater J. Hardy A. Virlouvet K. Maschke 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):435-443
The influence of linear defect boundaries on the transmission and scattering of elastic waves in quasi-two-dimensional wave-guides
is studied using the matching method. A linear defect boundary separating two wave-guide crystalline lattice domains is characterised
here by a linear chain of defect masses and by modified elastic constants in the boundary, different from their values in
the bulk of the domains. In particular a square lattice is considered to model the domains of the two-dimensional planar wave-guide
containing the linear defect. The reflection and transmission probabilities, and the total transmission probabilities are
calculated numerically and presented for the scattering processes in a variety of cases. We show that the interaction between
the localised modes introduced by the defect boundary and the propagating modes of the system leads to Fano resonances. These
resonances shift to higher (lower) frequencies for smaller (larger) defect masses, and for the same mass as function of the
angle of the incident wave. Other spectral features shown to exist are due to interference effects especially at oblique incidence
and when modifying the boundary elastic constants.
Received 8 November 1999 and Received in final form 14 January 2000 相似文献
2.
J. Kolehmainen S.M. Reimann M. Koskinen M. Manninen 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):731-736
We study the magnetic coupling in artificial molecules composed of two and four laterally coupled quantum dots. The electronic
ground-state configurations of such systems are determined by applying current spin density functional theory which allows
to include effects of magnetic fields. While the ground-state of a two-dot molecule with strong enough inter-dot coupling
tends to be antiferromagnetic with respect to the spins of the single dot components, we find that a square lattice of four
dots has a ferromagnetic ground state.
Received 17 February 1999 and Received in final form 1 June 1999 相似文献
3.
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
4.
P.Y. Friot P. Turban S. Andrieu M. Piecuch E. Snoeck A. Traverse E. Foy C. Theodorescu 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):41-50
This study is dedicated to the growth of bcc Mn by molecular beam epitaxy, in order to look at the magnetic properties of
bcc Mn near room temperature. For this purpose, Mn is deposited on bcc MxV1-x(001) alloy lattices (M = Fe or Nb) for which the lattice spacing is tunable by varying the concentration x. We first show that the parameter of the MxV1-x alloy's buffer layers can be adjusted from 2.95 ? to 3.3 ? depending on x and M. Three different structures in Mn films grown on these buffer layers are observed depending on the in-plane spacing
of the initial MxV1-x lattice. Thick Mn films are always found to grow epitaxially in the Mnstructure. For moderate thicknesses larger than 4 atomic planes, Mn grows in an unidentified structure. Finally, up to four
deposited atomic planes, Mn is found to grow in a tetragonal structure close to a bcc one on Fe(001), FexV1-x(001) and NbxV1-x(001) for . This tetragonal structure is shown to be a distorsion of a Mn bcc structure with . Except for ultra-thin Mn films deposited on Fe(001), no macroscopic magnetization is detected in our strained bcc Mn samples.
These results are compared to theoretical predictions.
Received 21 June 1999 相似文献
5.
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
6.
I. M. Catalano A. Cingolani M. Lepore R. Cingolani K. Ploog 《Il Nuovo Cimento D》1990,12(10):1465-1474
Summary The two-photon absorption spectra of GaAs/AlGaAs multiple quantum well and superlattice structures have been experimentally
investigated by means of the nonlinear luminescence technique in different polarization configurations. A strong excitonic
effect overlapping the interband two-photon spectrum has been found and the selection rules for the excitonic transitions
have shown to greatly change for different polarizations. The comparison of linear and nonlinear absorption measurements provides
important information on the excited states of excitons in multiple quantum wells.
Work partially supported by M.P.I. 相似文献
7.
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
8.
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
9.
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
10.
W.-Y. Ruan H.-F. Cheung 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):407-411
A coupled quantum dot system has been studied by numerical diagonalization of the Hamiltonian. Discontinuous ground-state
transitions induced by an external magnetic field have been predicted. Series of magic numbers of angular momentum which minimize
the ground-state electron-electron interaction energy have been discovered. Theoretical explanations derived from the first
principles have been formulated.
Received: 13 July 1997 / Accepted: 7 October 1997 相似文献
11.
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
12.
M. Glück A.R. Kolovsky H.J. Korsch N. Moiseyev 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):239-246
The paper discusses the metastable states of a quantum particle in a periodic potential under a constant force (the model
of a crystal electron in a homogeneous electric field), which are known as the Wannier-Stark ladder of resonances. An efficient
procedure to find the positions and widths of resonances is suggested and illustrated by numerical calculations for a cosine
potential, which are in excellent agreement with complex scaling resonance energies.
Received: 27 April 1998 / Revised: 21 July 1998 / Accepted: 3 August 1998 相似文献
13.
14.
Electronic structures in coupled two quantum dots by 3D-mesh Hartree-Fock-Kohn-Sham calculation 总被引:2,自引:0,他引:2
T. Matsuse T. Hama H. Kaihatsu N. Toyoda T. Takizawa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):391-394
To study the electronic structures of quantum dots in the framework of self-interaction-free including three dimensional effects,
we adopt the theory of nonlocal effective potential introduced by Kohn and Sham [#!ks65!#]. For utilizing the advantageous
point of the real space (3D) mesh method to solve the original nonlinear and nonlocal Hartree-Fock-Kohn-Sham (HFKS)-equation,
we introduce a linearization of the equation in the local form by introducing the local Coulomb potentials which depend on
explicitly the two single particle states. In practice, for solving the local form HFKS-equation, we use the Car-Parrinello-like
relaxation method and the Coulomb potentials are obtained by solving the Poisson equation under proper boundary conditions.
Firstly the observed energy gap between triplet- and singlet-states of N = 4 in DBS [#!tarucha96!#] is discussed to reproduce the addition energies and chemical potentials depending the magnetic
field. Next the coupling between two-quantum dots in TBS [#!aht97!#] is studied by adding the square barrier between two dots.
The spin-degeneracy [#!aht97!#] measured in gate-voltage depending on magnetic field is well reproduced in the limit of small
mismatch. Finally, the electronic states in the ring structure are calculated and discussed how the ring size and magnetic
field affect to the structures.
Received 30 November 2000 相似文献
15.
A. I. Belousova Yu. E. Lozovikb 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(2):251-264
A two dimensional (2D) classical system of dipole particles confined by a quadratic potential is studied. This system can
be used as a model for rare electrons in semiconductor structures near a metal electrode, indirect excitons in coupled quantum
dots etc. For clusters of N ≤ 80 particles ground state configurations and appropriate eigenfrequencies and eigenvectors for the normal modes are found.
Monte-Carlo and molecular dynamic methods are used to study the order-disorder transition (the “melting” of clusters). In
mesoscopic clusters (N < 37) there is a hierarchy of transitions: at lower temperatures an intershell orientational disordering of pairs of shells
takes place; at higher temperatures the intershell diffusion sets in and the shell structure disappears. In “macroscopic”
clusters (N > 37) an orientational “melting” of only the outer shell is possible. The most stable clusters (having both maximal lowest
nonzero eigenfrequencies and maximal temperatures of total melting) are those of completed crystal shells which are concentric
groups of nodes of 2D hexagonal lattice with a number of nodes placed in the center of them. The picture of disordering in
clusters is compared with that in an infinite 2D dipole system. The study of the radial diffusion constant, the structure
factor, the local minima distribution and other quantities shows that the melting temperature is a nonmonotonic function of
the number of particles in the system. The dynamical equilibrium between “solid-like” and “orientationally disordered” forms
of clusters is considered. 相似文献
16.
M. Sassetti F. Napoli B. Kramer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):643-654
Using the bosonization technique, a theory for the collective excitations of the interacting electrons in quantum wires with
two subbands occupied is developed. The dispersion relations for the inter-subband charge and spin density excitations are
determined. The results are used to interpret the features observed in recent measurements of the Raman spectra of AlGaAs/GaAs
quantum wires, particularly for photon energies near band gap resonance. It is shown that peaks previously identified as “single
particle excitations” are signatures of higher order collective spin density excitations. Predictions about the observability
of the interband modes are made.
Received 8 February 1999 相似文献
17.
Ken-Ichiro Imura 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):155-160
Effects of backward scattering between fractional quantum Hall (FQH) edge modes are studied. Based on the edge-state picture
for hierarchical FQH liquids, we discuss the possibility of the transitions between different plateaux of the tunneling conductance
G. We find a selection rule for the sequence which begins with a conductance (m: integer, p: even integer) in units of e
2/h. The shot-noise spectrum as well as the scaling behavior of the tunneling current is calculated explicitly.
Received 5 October 1999 and Received in final form 19 November 1999 相似文献
18.
B. Tanatar N. Mutluay 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):409-417
We study the spin correlations in two- and three-dimensional electron liquids within the sum-rule version of the self-consistent
field approach of Singwi, Tosi, Land, and Sj?lander. Analytic expressions for the spin-antisymmetric static structure factor
and the corresponding local-field correction are obtained with density dependent coefficients. We calculate the spin-dependent
pair-correlation functions, paramagnon dispersion, and static spin-response function within the present model, and discuss
the spin-density wave instabilities in double-layer electron systems.
Received: 22 September 1997 / Revised: 1 December 1997 / Accepted: 4 December 1997 相似文献
19.
M.V. Moskalets 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):645-649
The effect of an electrostatic energy (in the geometrical capacitance approach) on a persistent current is considered. It
is shown that at high temperatures the current amplitude shows periodic dips as a function of the potential difference between
a ring and a reservoir. These dips correspond to a lift of the Coulomb blockade. In a minimum of a dips a current is periodic
in a magnetic flux with a period at any temperatures.
Received: 6 April 1998 / Revised: 5 June 1998 / Accepted: 21 July 1998 相似文献
20.
D. Elefant G. Reiss C. Baier 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):45-53
On bulk layered single crystals (Bi0.25Sb0.75)2Te3 with a hole concentration cm-3 and a mobility cm2/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de
Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the
damping of the amplitudes with increasing temperature the cyclotron mass m
c
= 0.12m
0
is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The
weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected
as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection
with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the
bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide
with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier
reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be .
Received: 12 September 1997 / Revised: 8 January 1998 / Accepted: 22 January 1998 相似文献