共查询到20条相似文献,搜索用时 31 毫秒
1.
Xing-Tao An 《Physics letters. A》2008,372(45):6790-6796
Spin polarization in parallel double quantum dots embedded in arms of Aharonov-Bohm interferometer is investigated. The spin-orbit interaction exists in quantum dots. We find that the spin polarization is quite large even with a weak spin-orbit interaction. The direction and the strength of the spin polarization are well controllable and manipulatable by simply varying the strength of spin-orbit interaction or the energy levels in quantum dots. Moreover, electron-electron interaction strengthens the spin accumulation when the energy levels of the two quantum dots are identical. As the energy levels are unequal, electron-electron interaction cannot increase the spin accumulation. It is worth mentioning that the device is free of a magnetic field or a ferromagnetic material and it can be easily realized with present technology. 相似文献
2.
G. Duchateau E. Cormier R. Gayet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):191-196
A simple theoretical approach based on Coulomb-Volkov states is introduced to predict ionisation of atoms by intense laser
pulses in cases where the effective interaction time does not exceed one or two optical cycles [M. Nisoli et al., Opt. Lett. 22, 522 (1997)]. Under these conditions, the energy distributions of ejected electrons predicted by this non-perturbative approach
are in very good agreement with “exact" results obtained by a full numerical treatment. The agreement is all the better that
the principal quantum number of the initial state is high. For very strong fields, most electrons are ejected at an energy
which is close to the classical kinetic energy that would be transferred to free electrons by the electromagnetic field during
the pulse. The power of the present approach appears when keV. In this region, full numerical treatments become very lengthy and finally do not converge. However, the present Coulomb-Volkov
theory still makes reliable predictions in very short computer times.
Received 19 November 1999 and Received in final form 19 January 2000 相似文献
3.
J.H. Thywissen M. Olshanii G. Zabow M. Drndić K.S. Johnson R.M. Westervelt M. Prentiss 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):361-367
We describe how tightly confining magnetic waveguides for atoms can be created with microfabricated or nanofabricated wires.
Rubidium atoms guided in the devices we have fabricated would have a transverse mode energy spacing of K. We discuss the creation of a single-mode waveguide for atom interferometry whose depth is comparable to magneto-optical
trap (MOT) temperatures. We also discuss the application of microfabricated waveguides to low-dimensional systems of quantum
degenerate gases, and show that confinement can be strong enough to observe fermionization in a strongly interacting bosonic
ensemble.
Received 1st December 1998 and Received in final form 23 February 1999 相似文献
4.
J. Schmiedmayer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):57-62
By placing changeable nanofabricated structures (wires, dots, etc.) on an atom mirror one can design guiding and trapping potentials for atoms. These potentials are similar to the electrostatic
potentials which trap and guide electrons in semiconductor quantum devices like quantum wires and quantum dots. This technique
will allow the fabrication of nanoscale atom optical devices.
Received: 28 October 1997 / Revised: 17 February 1998 / Accepted: 17 July 1998 相似文献
5.
6.
Electronic structure of three-dimensional quantum dots 总被引:1,自引:0,他引:1
T. Vorrath R. Blümel 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):227-235
We study the electronic structure of three-dimensional quantum dots using the Hartree-Fock approximation. The confining potential
of the electrons in the quantum dot is assumed to be spatially isotropic and harmonic. For up to 40 interacting electrons
the ground-state energies and ground-state wavefunctions are calculated at various interaction strengths. The quadrupole moments
and electron densities in the quantum dot are computed. Hund's rule is confirmed and a shell structure is identified via the addition energies and the quadrupole moments. While most of the shell structure can be understood on the basis of the
unperturbed non-interacting problem, the interplay of an avoided crossing and the Coulomb interaction results in an unexpected
closed shell for 19 electrons.
Received 5 November 2001 / Received in final form 12 November 2002 Published online 1st April 2003
RID="a"
ID="a"e-mail: vorrath@physnet.uni-hamburg.de 相似文献
7.
M.V. Moskalets 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):523-529
The peculiarities of a low temperature heat transfer through a ballistic quantum dot (a double potential barrier) with interacting
leads due to a long-range Coulomb interaction (in the geometrical capacitance approach) are considered. It is found that the
thermal conductance K shows periodic peaks as a function of the electrostatic potential of a dot at low temperatures. At the peak maximum it is
whereas near the minimum it is . Near the peak maximum the dependence K(T) is essentially nonmonotonic at the temperatures correspondent to the level spacing in the quantum dot.
Received 20 October 1999 and Received in final form 20 January 2000 相似文献
8.
A. Milekhin N.P. Stepina A.I. Yakimov A.I. Nikiforov S. Schulze D.R.T. Zahn 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):355-359
Self-organised Ge dot superlattices grown by molecular beam epitaxy of Ge and Si layers utilizing Stranski-Krastanov growth
mode were investigated by Raman spectroscopy. An average size of Ge quantum dots was obtained from transmission electron microscopy
measurements. The strain and interdiffusion of Ge and Si atoms in Ge quantum dots were estimated from the analysis of frequency
positions of optical phonons observed in the Raman spectra. Raman scattering by folded longitudinal acoustic phonons in the
Ge dot superlattices was observed and explained using of elastic continuum theory.
Received 25 January 2000 相似文献
9.
M. Manninen M. Koskinen S.M. Reimann B. Mottelson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):381-385
Exact many-body methods as well as current-spin-density functional theory are used to study the magnetism and electron localization
in two-dimensional quantum dots and quasi-one-dimensional quantum rings. Predictions of broken-symmetry solutions within the
density functional model are confirmed by exact configuration interaction (CI) calculations: In a quantum ring the electrons
localize to form an antiferromagnetic chain which can be described with a simple model Hamiltonian. In a quantum dot the magnetic
field localizes the electrons as predicted with the density functional approach.
Received 5 December 2000 相似文献
10.
Quantum dots with a three-dimensional confining potential, i.e. “spherical” quantum dots, are considered with inclusion of
electron-electron interaction (a quantum analog of the Thomson atom). The energy spectrum of two-electron parabolic quantum
dots has been determined by numerical diagonalization of the full Hamiltonian in a one-particle basis.
Fiz. Tverd. Tela (St. Petersburg) 40, 2134–2135 (November 1998) 相似文献
11.
Yu. E. Lozovik V. D. Mur N. B. Narozhnyi 《Journal of Experimental and Theoretical Physics》2003,96(5):932-939
A new method is proposed for calculating the energy spectrum and the wave functions of N-electron quantum dots with an arbitrary confining potential. The method consists in expansion with respect to a dimensionless quantum parameter 1/Q, which is expressed in terms of the ratio of the characteristic Coulomb energy of electron-electron interaction to the characteristic energy of one-particle transition in a confining potential. Two-electron quantum dots with a parabolic confining potential in an external magnetic field are considered. Strongly correlated states of the system and the spin rearrangement in a strong magnetic field are analyzed. Analytic expressions are obtained for the energy and the wave functions of the system. It is shown that restriction of the analysis only to the first three terms in the quantum-parameter expansion gives an accuracy of one percent when calculating the energy even for values of Q on the order of unity, i.e., for the presently implementable GaAs quantum dots. The expressions for energy obtained are in a good agreement with the experimental data for quantum dots in a perpendicular magnetic field. 相似文献
12.
F. Selva J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(3):441-449
We study the difference between on site Hubbard and long range Coulomb repulsions for two interacting particles in a disordered
chain. The system size L (in units of the lattice spacing) is of the order of the one particle localization length and the energies are taken near
the band center. In the two cases, the limits of weak and strong interactions are characterized by uncorrelated energy levels
and are separated by a crossover regime where the states are more extended and the spectra more rigid. U denoting the interaction strength and t the kinetic energy scale, the crossovers take place for interaction energy to kinetic energy ratios U/t and U/(2tL) of order one, for Hubbard and Coulomb repulsions respectively. While Hubbard repulsion can only yield weak critical chaos
with intermediate spectral statistics, Coulomb repulsion can drive the two particle system to quantum chaos with Wigner-Dyson
spectral statistics. The interaction matrix elements are studied to explain this difference.
Received 21 March 2000 and Received in final form 5 February 2001 相似文献
13.
Richard J. Warburton 《Contemporary Physics》2013,54(5):351-353
Quantum dots are nanometre-sized clusters of semiconductor material which confine electrons in all three directions. The physics of quantum dots are dominated by quantization: there are discrete energy levels, as in real atoms. Quantum dots can now be self-assembled directly in the growth of inorganic semiconductors, and this discovery has fuelled an explosion in the interest in this field. A review of some of this work is presented, concentrating on the optical properties of quantum dots, and possible applications for photonic devices. 相似文献
14.
Neerja A.N. Tripathi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(1):5-10
We present calculations of differential, integrated elastic, total, momentum transfer cross-sections and spin-polarization
parameters S, T and U for scattering of electrons from Eu and Bi atoms in the energy range 2.0 to 500.0 eV using semi-relativistic approach. The
target-projectile interaction is represented both by real and complex parameter-free optical potentials in the solution of
Dirac equation for the scattered electrons. The results for the differential cross-sections and spin-polarization parameters
have been compared with the available calculations and experimental results.
Received 17 February 2000 and Received in final form 15 June 2000 相似文献
15.
We study magnetism in magnetically doped quantum dots as a function of the confining potential, particle numbers, temperature, and strength of the Coulomb interactions. We explore the possibility of tailoring magnetism by controlling the nonparabolicity of the confinement potential and the electron-electron Coulomb interaction, without changing the number of particles. The interplay of strong Coulomb interactions and quantum confinement leads to enhanced inhomogeneous magnetization which persists at higher temperatures than in the noninteracting case. The temperature of the onset of magnetization can be controlled by changing the number of particles as well as by modifying the quantum confinement and the strength of the Coulomb interactions. We predict a series of electronic spin transitions which arise from the competition between the many-body gap and magnetic thermal fluctuations. 相似文献
16.
S. Teuber T. Döppner T. Fennel J. Tiggesbäumker K.H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):59-63
The photoionization of metal clusters in intense femtosecond laser fields has been studied. In contrast to an experiment on
atoms, the interaction in this case leads to a very efficient and high charging of the particle where tens of electrons per
atom are ejected from the cluster. The recoil energy distribution of the atomic fragment ions was measured which in the case
of lead clusters exceeds 180 keV. Enhanced charging efficiency which we observed earlier for specific pulse conditions is
not reflected in the recoil energy spectra. Both the average and the maximum energies decrease with increasing laser pulse
width. This is in good agreement with molecular dynamics calculations.
Received 20 December 2000 相似文献
17.
S. Tarucha D.G. Austing S. Sasaki Y. Tokura W. van der Wiel L.P. Kouwenhoven 《Applied Physics A: Materials Science & Processing》2000,71(4):367-378
The effects of direct Coulomb and exchange interactions on spin states are studied for quantum dots contained in circular
and rectangular mesas. For a circular mesa a spin-triplet favored by these interactions is observed at zero and nonzero magnetic
fields. We tune and measure the relative strengths of these interactions as a function of the number of confined electrons.
We find that electrons tend to have parallel spins when they occupy nearly degenerate single-particle states. We use a magnetic
field to adjust the single-particle state degeneracy, and find that the spin-configurations in an arbitrary magnetic field
are well explained in terms of two-electron singlet and triplet states. For a rectangular mesa we observe no signatures of
the spin-triplet at zero magnetic field. Due to the anisotropy in the lateral confinement single-particle state degeneracy
present in the circular mesa is lifted, and Coulomb interactions become weak. We evaluate the degree of the anisotropy by
measuring the magnetic field dependence of the energy spectrum for the ground and excited states, and find that at zero magnetic
field the spin-singlet is more significantly favored by the lifting of level degeneracy than by the reduction in the Coulomb
interaction. We also find that the spin-triplet is recovered by adjusting the level degeneracy with magnetic field.
Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000 相似文献
18.
R. Pino A.J. Markvoort P.A.J. Hilbers 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(1):103-106
An exactly solvable local Thomas-Fermi-Dirac approximation is applied to the calculation of the ground-state density of three-dimensional
quantum dot arrays, where we give estimates to properties like total energy, chemical potential, and differential capacitance.
Numeric examples are calculated for pairs of quantum dots using a Gaussian confining potential. The computational complexity
of the present method is linear in the number of electrons and centers of the system. 相似文献
19.
M. Leadbeater R. Raimondi P. Schwab C. Castellani 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):277-281
We report on the non-linear electric field effect in the conductivity of disordered conductors. We find that the electron-electron
interaction in the particle-hole triplet channel strongly affects the non-linear conductivity. The non-linear effect introduces
a field dependent temperature scale TE and provides a microscopic mechanism for electric field scaling at the metal-insulator transition. We also study the magnetic
field dependence of the non-linear conductivity and suggest possible ways to experimentally verify our predictions. These
effects offer a new probe to test the role of quantum interference at the metal-insulator transition in disordered conductors.
Received 9 February 2000 相似文献
20.
N. V. Bondar’ 《Optics and Spectroscopy》2010,108(5):728-734
Samples of borosilicate glasses doped by CdS with concentrations smaller than 1% are studied. It is shown that, due to a disorder
at interfaces of quantum dots, the main channels of emission of excitons by quantum dots are the annihilation of excitons
in quantum and localized surface states, while the efficiency of interaction between the channels largely depends on the radius
of quantum dots. It is found for the first time that states that form the second emission channel are not discrete energy
levels in the band gap, as is usually assumed in some experimental and theoretical works, but rather form a quasi-continuous
tail of the density of localized states. These localized states appear as a result of dangling bonds of outer atoms of quantum
dots. Energy relaxation of carriers via localized states is the reason for a long response time of these structures to an
external action and can be enhanced due to a polarization effect caused by different dielectric constants of materials of
quantum dots and matrix. 相似文献