共查询到20条相似文献,搜索用时 15 毫秒
1.
We considered the propagation of laser monochromatic radiation in a superlattice that contains regions with an elevated concentration
of carriers. The model of the energy spectrum of electrons is chosen in the strong coupling approximation. The electromagnetic
field is described quasiclassically with Maxwell equations, which, as applied to the problem under study, are reduced to a
non-one-dimensional sine-Gordon wave equation for the vector-potential. We analyzed the wave equation in the approximation
of slowly varying amplitudes and phases and obtained and numerically solved an effective equation that describes the electromagnetic
field in the superlattice. We studied different regimes of propagation of laser radiation, analyzed diffraction by regions
with an elevated electron concentration. 相似文献
2.
Proposal of a Microwave-Driven Semiconductor Superlattice Oscillator for Generation of THz Radiation
F. Klappenberger K. F. Renk 《International Journal of Infrared and Millimeter Waves》2004,25(3):429-438
We present the proposal of a microwave-driven semiconductor superlattice oscillator. We show that the interplay of a microwave pump field with a synchronous harmonic field can make a semiconductor superlattice to a gain medium for the harmonic field. Placing the superlattice in a resonator for the harmonic field allows the operation of an oscillator. The gain mechanism is based on Bloch oscillations of miniband electrons. The gain is mediated either by the interaction of the high-frequency field with the single electrons or with space charge domains or with both. The microwave-driven superlattice oscillator should be suitable for generation of coherent radiation up to several THz. 相似文献
3.
Electrons in a superlattice at high fields are suitably described in terms of localized states related to the potential wells. Conduction is dominated by transitions between adjacent wells if the potential drop over a superlattice period exceeds the width of the lowest miniband. It is shown that the probability of these transitions, and consequently the current as well, decrease with increasing field. This effect originates from decreasing overlap between electron states of neighbouring wells, and it is found for the interaction with acoustic phonons and with impurities as well. 相似文献
4.
The conductivity of a semiconductor superlattice in a magnetic field perpendicular to the superlattice axis is calculated. The dependence of the conductivity on the magnetic field strength is studied. It is found that there is a magnetic-field range where the resistivity is proportional to the magnetic field strength. 相似文献
5.
The action of a strong high-frequency electromagnetic field on a lateral semiconductor superlattice is considered based on the quasi-classical electron transport theory in the self-consistent wave formulation. The theory predicts that a lateral superlattice can emit terahertz radiation wave trains, which are associated with periodic excitation of Bloch oscillations in the superlattice arising because of the development of transient processes in it in a variable self-consistent electric field. The conditions necessary for observing Bloch oscillator radiation were found. The spectral composition of radiation transmitted through the superlattice and the energy efficiency of frequency multiplication related to Bloch oscillator excitation were calculated. 相似文献
6.
Interaction between an rf electromagnetic field and the Fe/Cr superlattice placed in a rectangular waveguide so that a high-frequency
current passes in the plane of superlattice layers is considered. The transmission coefficient versus the magnetic field strength
is found at centimeter waves, and a correlation between this dependence and the field dependence of the dc magnetoresistance
is established. It is shown that a change in the transmission coefficient may greatly exceed the giant magnetoresistance of
the superlattice. The frequency dependence of the microwave measurements has an oscillatory character. The oscillation frequencies
are analyzed in terms of wavelet transformation. Two types of oscillation periods are found to exist, one of which corresponds
to the resonance of waves traveling in the superlattice along the direction parallel to the narrow wall of the waveguide. 相似文献
7.
S. Bujkiewicz C. R. Tench T. M. Fromhold M. J. Carter F. W. Sheard L. Eaves 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
The semiclassical motion of an electron along the axis of a superlattice may be calculated from the miniband dispersion curve. Under a weak electric field the electron executes Bloch oscillations which confines the motion along the superlattice axis. When a magnetic field, tilted with respect to the superlattice axis, is applied the electron orbits become chaotic. The onset of chaos is characterised by a complex mixed stable-chaotic phase space and an extension of the orbital trajectories along the superlattice axis. This delocalisation of the orbits is also reflected in the quantum eigenstates of the system some of which show well-defined patterns of high probability density whose shapes resemble certain semiclassical orbits. This suggests that the onset of chaos will be manifest in electron transport through a finite superlattice. We also propose that these phenomena may be observable in the motion of trapped ultra-cold atoms in an optically induced superlattice potential and magnetic quadrupole potential whose axis is tilted relative to the superlattice axis. 相似文献
8.
《Physics letters. A》1999,255(3):178-182
We calculate the magnetostatic surface mode of a lateral-magnetic superlattice, with an antiferromagnetic interlayer coupling, which is described with an effective medium theory. We find analytically that there is a critical value of the external field for the surface mode, and there are some interesting properties from the frequency of the surface mode as a function of the propagation angle and external field. 相似文献
9.
A method to calculate the spectrum of the Lyapunov exponents for a periodic semiconductor nanostructure (superlattice) described in the framework of a semiclassical approach is proposed. The analysis of the stability of a stationary state in such a system is performed for autonomous dynamics and in the presence of a tilted magnetic field. The method of the Lyapunov exponents is used to study the effect of the tilted magnetic field on the stability of the stationary state and the characteristics of subterahertz oscillation regimes. 相似文献
10.
F. Ş. Boydağ Sh. V. Mamedov V. A. Alekperov Y. Lenger Özcanli 《Optics and Spectroscopy》2003,95(2):225-229
The interaction between a solitary electromagnetic wave and a narrow layer with an increased electron concentration in a semiconductor superlattice in a preset uniform alternating electric field directed along the superlattice axis is investigated. The model of the electron energy spectrum in the superlattice is chosen in the strong coupling approximation taking into account the second harmonic. It is shown that, for certain relations between the amplitude and frequency of the alternating electric field, a solitary electromagnetic wave approaching the layer with an increased electron concentration can be trapped by this layer. 相似文献
11.
研究了基于硅烯的静电势超晶格、铁磁超晶格、反铁磁超晶格中谷极化、自旋极化以及赝自旋极化的输运性质,分析了铁磁交换场、反铁磁交换场以及化学势对输运性质的影响,讨论了电场对谷极化、自旋极化以及赝自旋极化的调控作用.结果表明:当3种超晶格的晶格数达到10以上时,在硅烯超晶格中很容易实现100%的谷极化、自旋极化和赝自旋极化,而且通过调节超晶格上的外加电场可以使极化方向发生翻转,从而在硅烯超晶格中实现外电场对谷自由度、自旋自由度以及赝自旋自由度的操控. 相似文献
12.
Two-dimensional electron gas systems modulated by a lateral magnetic superlattice are proposed and the related magnetoresistance effect is described in this work. It is found that the magnetoresistance (MR) ratio of the given structures depends strongly on the uniform magnetic field, and the peaks of the MR ratio depressed linearly with the increase of the uniform magnetic field. This feature can be utilized in practical linear magnetoresistance (LMR) devices. 相似文献
13.
A. B. Rinkevich L. N. Romashev V. V. Ustinov 《Journal of Experimental and Theoretical Physics》2000,90(5):834-841
The rf magnetoresistance of Fe/Cr superlattices is studied for two orientations of the current: parallel and across the superlattice layers. A mutually single-valued correspondence is established between the relative magnetoresistance measured at dc current and the change in the transmission coefficient of electromagnetic waves in the magnetic field. When rf currents flow across the layers, the relative change in the signal amplitude is proportional to twice the change in the electrical resistance of the superlattice and is of opposite sign. It is shown that the rf losses are determined by the surface resistance which is proportional to the superlattice thickness and inversely proportional to its conductivity. An equation is derived for the rf electric field distribution in the superlattice. It is established that when the thickness of the superlattice is small compared with the skin layer depth, field and current components which penetrate through the entire superlattice exist. 相似文献
14.
15.
T. Feil H.-P. Tranitz C. Gerl W. Wegscheider 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):301
We experimentally investigate the transport through a shunted surface superlattice under the influence of a magnetic field applied perpendicular to the current direction. The current–voltage characteristics of these surface superlattices exhibit a peak which is followed by a wide region of negative differential resistance. The application of a transverse magnetic field has a profound influence on the position and height of this peak. The recorded shifts are compared to the predictions of different superlattice transport theories. Since these theories predict a different dependence on the magnetic field strength, the transport mechanism in the surface superlattice structures can be uniquely determined. 相似文献
16.
S. V. Kryuchkov E. I. Kukhar M. N. Zolotykh 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(12):1582-1584
The effect of a constant electric field on the charge dragging by an electromagnetic wave is studied for graphene-based superlattice.
An expression is derived for the electric current density in a graphene-based superlattice under a constant electric field
in an approximation of a constant time of relaxation. It is demonstrated that the current as a function of wave intensity
is of a nonmonotonous character. 相似文献
17.
18.
Spin flop transition in a finite antiferromagnetic superlattice: evolution of the magnetic structure
An antiferromagnetic (AF) superlattice of Fe/Cr(211) is used as a model system to study magnetic transitions in a finite-size geometry. With polarization neutron reflectometry the magnetic structure at the surface spin-flop transition and its evolution with field is determined. A domain wall created near the surface penetrates the superlattice with increasing field, splitting it into two antiphase, AF domains. After reaching the center the spin-flopped phase spreads throughout the superlattice. The experimental results are in substantial agreement with theoretical and numerical predictions. 相似文献
19.
A theoretical study of harmonic generation in a short period AlGaN/GaN superlattice induced by a terahertz field
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Based on an improved energy dispersion relation, the
terahertz field induced nonlinear transport of miniband electrons in
a short period AlGaN/GaN superlattice is theoretically studied in
this paper with a semiclassical theory. To a short period
superlattice, it is not precise enough to calculate the energy
dispersion relation by just using the nearest wells in tight binding
method: the next to nearest wells should be considered. The results
show that the electron drift velocity is 30% lower under a dc
field but 10% higher under an ac field than the traditional
simple cosine model obtained from the tight binding method. The
influence of the terahertz field strength and frequency on the
harmonic amplitude, phase and power efficiency is calculated. The
relative power efficiency of the third harmonic reaches the peak
value when the dc field strength equals about three times the
critical field strength and the ac field strength equals about four
times the critical field strength. These results show that the
AlGaN/GaN superlattice is a promising candidate to convert radiation
of frequency ω to radiation of frequency 3ω or even
higher. 相似文献
20.
E. I. Kukhar’ S. V. Kryuchkov E. S. Ionkina 《Bulletin of the Russian Academy of Sciences: Physics》2017,81(1):47-50
Longitudinal and transverse high-frequency conductivities of a graphene superlattice placed in an additional dc electric field are calculated. It is shown that in a sufficiently strong transverse field, the dependence of the longitudinal high-frequency conductivity of the superlattice on the ac field frequency changes. This effect is explained by the nonadditivity of the electronic spectrum of the investigated structure. 相似文献