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31.
32.
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
33.
Resonance split of ballistic conductance peaks in electric and magnetic superlattices 总被引:1,自引:0,他引:1
Z.Y. Zeng L.D. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):389-392
Resonant peak splitting for ballistic conductance in finite electric superlattices (ES) and magnetic superlattices (MS) was
investigated theoretically. It is shown that, for electron tunneling through the ES (MS) of identical n electric (magnetic) barriers, the resonance split of the conductance peak is (n–1)-fold; while for electron tunneling through the ES (MS) made of two different barriers, one resonant window of the former
splits into two subwindows, within each of which the resonance split is (m–1)-fold, where m is the number of the renormalized building blocks consisting of two different barriers of the latter.
Received 15 February 2000 相似文献
34.
U. Pustogowa C. Blaas C. Uiberacker J. Zabloudil P. Weinberger L. Szunyogh C. Sommers 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(4):653-658
The magnetic properties of (ConPdm)r superstructures on Pd(100) and Pd(111) are evaluated using the fully-relativistic spin-polarized screened Korringa-Kohn-Rostoker
method. It is found that only in the case of a Pd(111) substrate such superstructures exhibit perpendicular magnetism, while
on a Pd(100) substrate the magnetization is oriented in-plane. Also investigated is the effect of interdiffusion in repeated
superstructures. By using the inhomogeneous coherent potential approximation (CPA) for layered systems the effect of ordering
into (repeated) superstructures can be described in an ab-initio-like manner. It is found that already small amounts of interdiffusion can be decisive for the actual value of the magnetic
anisotropy energy.
Received 3 November 1999 and Received in final form 18 January 2000 相似文献
35.
Jian-Min Shi V.N. Freire G.A. Farias 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):337-348
A theoretical study is performed on the confined electron and shallow donor states properties in graded GaAs/AlxGa1-xAs spherical quantum dots. The two lowest energy levels of a confined electron are obtained taking into account the dependence
of the electron effective mass on the spatial profile of the Al molar fraction. The ground state of a single Si shallow donor,
which may be located at an arbitrary position in the structure, is calculated through a variational approach. Depending on
the dot interface width and localization, we find that the energy levels of the electron and donor states for the system under
study can be blue or red shifted appreciably in comparison to those calculated within the sharp interface picture. We show
that it is necessary to have accurate information concerning the interface of semiconductor dots whose samples are used in
the experiments, in order to achieve a better understanding of their optical properties.
Received 31 May 1999 相似文献
36.
A novel digestive ripening process is shown to narrow the particle size distribution from a highly polydisperse dodecanethiol ligated gold colloid. Unlike the Ostwald ripening process, the digestion occurs through transferring materials from large particles to small particles. Temperature-induced size segregation can further select the particle sizes. By using these two methods, highly ordered superlattices using nanocrystals as building blocks can be synthesized directly from a polydisperse colloid. 相似文献
37.
M. Schöck C. Sürgers H. v. Löhneysen 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):1-10
The superconducting and magnetic properties of Nb/Pd1-xFex/Nb triple layers with constant Nb layer thickness dNb=200 ? and different interlayer thicknesses 3 ?≤ dPdFe ≤ ? are investigated. The thickness dependence of the magnetization and of the superconducting transition temperature shows
that for small iron concentration x the Pd1-xFex layer is likely to be in the paramagnetic state for very thin films whereas ferromagnetic order is established for x ≥ 0.13.
The parallel critical field Bc2||(T){B_{c2||}}(T) exhibits a transition from two-dimensional (2D) behavior where the Nb films are coupled across the interlayer, towards a
2D behavior of decoupled Nb films with increasing dPdFeand/or x. This transition allows a determination of the penetration depth xF{\xi _F} of Cooper pairs into the Pd1-xFex layer as a function of x. For samples with a ferromagnetic interlayer xF{\xi _F} is found to be independent of x. 相似文献
38.
在超晶格样品(GaAs)4/(AlAs)2的一级共振拉曼光谱的界面模的观察中,四个界面模在XX和XY两种偏振态中均能被观察到,这与传统的选择定则相矛盾。这是因为传统的理论假设电子波函数是完全限制在势阱当中,而在超薄系统中例如在GaAs势阱中的电子波函数会穿透到AlAs势垒中,从而得到新的结果。这表明传统的理论在被应用到超薄系统或超小系统时需要进行一定的修正。 相似文献
39.
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
40.
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