共查询到20条相似文献,搜索用时 15 毫秒
1.
L. Berthier J. L. Barrat J. Kurchan 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):635-641
We calculate analytically the conditions that establish the number of bound states in finite superlattices as a function of
the depth, width and separation of the wells. We consider a lattice of -wells and a set of rectangular wells. For this latter case, we show how for finite systems the energy levels already group
together in bands separated by gaps.
Received 24 April 1998 相似文献
2.
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
3.
4.
H. Kellay J. Rouch 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):121-129
In this paper we study the influence of the magneto-coupling effect between the longitudinal motion component and the transverse
Landau orbits of an electron on transmission features in single barrier structures. Within the parabolic conduction-band approach,
a modified one-dimensional effective-mass Schr?dinger equation, including the magneto-coupling effect generated from the position-dependent
effective mass of the electron, is strictly derived. Numerical calculations for single barrier structures show that the magneto-coupling
effect brings about a series of the important changes for the transmission probability, the above-barrier quasi-bound states,
and the tunneling time. Through examining the variation of the above-barrier resonant-transmission spectrum with the barrier
width and observing the well-defined Lorentzian line-shape of the above-barrier resonant peaks, we convincingly show that
the above-barrier resonant transmission in single barrier structures is delivered by the above-barrier quasibound states in
the barrier region, just as the below-barrier resonant tunneling in double barrier structures is mediated by the below-barrier
quasi-bound states in the well. Furthermore, we come to the conclusion that the magneto-coupling effect brings about not only
the splitting of the above-barrier quasi-bound levels but also the striking reduction of the level-width of the quasi-bound
states, correspondingly, the substantial increase of the density of the quasi-bound states. We suggest that magneto-coupling
effects may be observed by the measurements of the optical absorption spectrum associated with the above-barrier quasi-bound
states in the single barrier structures.
Received: 26 September 1997 / Revised: 26 November 1997 / Accepted: 15 December 1997 相似文献
5.
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
6.
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
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.
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
9.
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
10.
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
11.
H.-K. Zhao J. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):513-524
The time-dependent transport through an ultrasmall quantum dot coupling to two electron reservoirs is investigated. The quantum
dot is perturbed by a quantum microwave field (QMF) through gate. The tunneling current formulae are obtained by taking expectation
values over coherent state (CS), and SU(1,1) CS. We derive the transport formulae at low temperature by employing the nonequilibrium
Green function technique. The currents exhibit coherent behaviors which are strongly associated with the applied QMF. The
time-dependent currents appear compound effects of resonant tunneling and time-oscillating evolution. The time-averaged current
and differential conductance are calculated, which manifest photon-assisted behaviors. Numerical calculations reveal the similar
properties as those in classical microwave field (CMF) perturbed system for the situations concerning CS and squeezed vacuum
SU(1,1) CS. But for other squeezed SU(1,1) CS, the tunneling behavior is quite different from the system perturbed by a single
CMF through gate. Due to the quantum signal perturbation, the measurable quantities fluctuate fiercely.
Received 28 May 1998 相似文献
12.
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
13.
F. Milde R.A. Römer M. Schreiber V. Uski 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):685-690
We study the three-dimensional Anderson model of localization with anisotropic hopping, i.e., weakly coupled chains and weakly coupled planes. In our extensive numerical study we identify and characterize the metal-insulator
transition by means of the transfer-matrix method. The values of the critical disorder obtained are consistent with results of previous studies, including multifractal analysis of the wave functions and energy-level
statistics. decreases from its isotropic value with a power law as a function of anisotropy. Using high accuracy data for large system
sizes we estimate the critical exponent as . This is in agreement with its value in the isotropic case and in other models of the orthogonal universality class.
Received 25 October 1999 相似文献
14.
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
15.
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
16.
P. V. Aleskandrova V. K. Gueorguiev Tz. E. Ivanov J. B. Koprinarova 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):453-457
Leakage currents through Al/ZrO2/SiO2/n-Si metal-insulator-semiconductor (MIS) capacitors were studied. Thin SiO2 films were chemically grown on monocrystalline phosphorous doped silicon wafers. Zirconia films with thicknesses of 15 and
50 nm were
deposited by radio frequency (rf) magnetron sputtering and, then,
annealed in oxygen ambient at 850 ○C, for 1 h. The dielectric constant
of the sputtered and annealed ZrO2 layer was of about 17.8. The
equivalent oxide thickness (EOT) of the stack 15 nm and 50 nm-ZrO2/SiO2 structure was estimated to be 3.2 nm and 10.7 nm, respectively. The temperature dependence of the leakage currents was explained
by Poole-Frenkel (PF) conduction mechanism. Shallow trap levels in the studied structure of about 0.2 eV and 0.46 eV were
calculated. The existence of A and D-defects, due to the sputtering and high temperature annealing in oxygen, was suggested. 相似文献
17.
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
18.
In the asymptotic limit, the interlayer exchange coupling decays as D-2, where D is the spacer thickness. A systematic procedure for calculating the preasymptotic corrections, i.e., the terms of order D-n with ,is presented. The temperature dependence of the preasymptotic corrections is calculated. The results are used to discuss
the preasymptotic corrections for the Co/Cu/Co(001) system.
Received 7 January 1999 相似文献
19.
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
20.
Z.Y. Zeng Y. Xiang L.D. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):699-705
We proposed a new kind of coupled coaxial cylindrical quantum wires structure - quantum cable, and calculated its single-electron
energy subband spectrum for the varying structure parameters, in order to investigate its subband motion in the structure
parameter space. It is shown that quantum cable has unique subband spectrum, which differs either from the (solid and hollow)
cylindrical quantum wire or from the usual coupled double quantum wires (CDQWs) structure. Aside from the two-fold degeneracy
induced by the cylindrical symmetry, crossings (accidental degeneracies) and anticrossings (repulsions) of quantum cable subbands
with different azimuthal and radial quantum numbers are observed as one of the cable structure parameters varies. This introduces
the dependence of the subband ladder on the structure parameters of the quantum cable structure. However, the subband with
the lowest azimuthal and radial quantum numbers remains the lowest subband and never crosses with the other subbands irrespective
of the value of structure parameters. As the coupling barrier is broadening (coupling becoming weak), some subbands bundling
toward another subband is seen before the extreme isolating limit achieved. Moreover, the separation between neighboring subbands
exhibits non-monotonous evolution as one changes the thickness of one of the cylindrical quantum wires, with a minimum existing
in the separation between some two adjacent subbands. Interesting optical and transport phenomena arising from these unique
subband properties of the quantum cable structure are also predicted.
Received 22 March 2000 and Received in final form 6 June 2000 相似文献