Effect of the charge dragging in a graphene-based superlattice under a constant electric field

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.     

Superlattice conductivity sign change induced by intense electromagnetic radiation

The current density in a superlattice exposed to a quantizing electric field and the terahertz field has been calculated. The calculations have been carried out taking into account inelastic scattering of charge carriers by phonons. The possibility of an absolute negative conductivity, i.e., the emergence of electric current opposing the direction of the quantizing electric field, has been demonstrated.     

Nanosecond dynamics of ferroelectric/dielectric superlattices

The nanosecond response of a PbTiO(3)/SrTiO(3) ferroelectric/dielectric superlattice to applied electric fields is closely linked to the dynamics of striped domains of the remnant polarization. The intensity of domain satellite reflections observed with time-resolved x-ray microdiffraction decays in 5-100 ns depending on the magnitude of the electric field. The piezoelectric response of the superlattice within stripe domains is strongly suppressed due to electromechanical clamping between adjacent regions of opposite polarization. Regions of the superlattice that have been switched into a uniform polarization state by the applied electric field, however, exhibit piezoelectricity during the course of the switching process. We propose a switching model different from previous models of the switching of superlattices, based instead on a spatially heterogeneous transformation between striped and uniform polarization states.     

The Franz-Keldysh effect in superlattices in the field of a nonlinear electromagnetic wave

We study the effect of interminiband breakdown in a semiconductor quantum superlattice in a constant electric field and in the field of a nonlinear wave whose intensities are directed along the superlattice axis. The problem has been solved in the quasiclassical approximation for an arbitrary ratio between the widths of the allowed and forbidden minibands. In particular cases, we have obtained formulas for the breakdown probability in the presence of only one field, as well as for a linear wave and a solitary wave (soliton). It is shown that the probability of interminiband breakdown increases with the nonlinearity parameter of the electromagnetic wave k. The absorption coefficient of the nonlinear wave is calculated for typical parameters of the superlattice. Pedagogical University, Volgograd, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 6, pp. 758–766, June, 1998.     

Radioelectric effect in a superlattice under the action of an elliptically polarized electromagnetic wave

The density of the current associated with the drag of charge carriers in a superlattice by an elliptically polarized electromagnetic wave is calculated. Two cases of the mutual orientation of the Umov-Poynting vector and the superlattice axis, i.e., their parallel and perpendicular orientations, are analyzed. It is shown that, for the parallel orientation, the radioelectric effect can change sign. The influence of the longitudinal dc electric field on the radioelectric effect is investigated under the conditions where a circularly polarized electromagnetic wave propagates along the superlattice axis. The current density is studied as a function of the electric field strength and the electromagnetic wave intensity. It is demonstrated that the direction of the electric current is changed at specific values of the dc field strength and the wave intensity.     

Transport in superlattices in the stark ladder regime

The current-voltage characteristic of a semiconductor superlattice in the Stark ladder regime has been calculated. It is shown that the negative differential conductivity onset electric field is defined by the scattering time, which depends only very slightly on the superlattice miniband width.     

Effect of a dc electric field on the high-frequency conductivity of a graphene superlattice

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.     

Soliton delay line based on a semiconductor superlattice

A new type of delay line intended for soliton pulses is proposed. As a nonlinear medium, a semiconductor superlattice is taken. Solitons that propagate along the superlattice layers are confined in cells bounded by transverse inhomogeneity layers. Solitons are confined and released with the help of an external electric current passing inside the cell.     

Ratchet effects in quantum wells with a lateral superlattice

Experimental and theoretical works on the ratchet effects in quantum wells with a lateral superlattice excited by alternating electric fields of terahertz frequency range has been reviewed. We discuss the Seebeck ratchet effect and helicity driven photocurrents and show that the photocurrent generation is based on the combined action of a spatially periodic in-plane potential and a spatially modulated light.     

Electric-field distribution in a quantum superlattice with an injecting contact: Exact solution

A very simple model describing steady-state electron transport along a quantum superlattice of a finite length taking into account an arbitrary electrical characteristic of the injecting contact is considered. In the singleminiband approximation, exact formulas for the spatial distribution of the electric field in the superlattice are derived for different types of contact. Conditions under which the field is uniform are identified. Analytical expressions for the current–voltage characteristics are obtained. In the context of the developed theory, the possibility of attaining uniform-field conditions in a diode structure with a natural silicon-carbide superlattice is discussed.     

Staggered excitonic resonances of Stark-ladder transitions in an asymmetric double-well GaAs/AlAs superlattice

Excitonic effects on Stark-ladder transitions have been investigated experimentally and theoretically in a novel asymmetric double-well superlattice consisting of wide and narrow GaAs quantum wells separated by a constant AlAs barrier. In this superlattice strong electron resonance can occur under the applied electric field between the wide and narrow wells. It is found that due to existence of the two different heavy-hole localized states two types of excitonic resonances which are staggered in field are observed in the low-temperature photocurrent spectra. This field difference in the staggered exciton resonances is rigorously explained by variational calculations of the changes in the direct and indirect exciton binding energies with the field.     

Drastic reduction of shot noise in semiconductor superlattices

We have found experimentally that the shot noise of the tunneling current I through an undoped semiconductor superlattice is reduced with respect to the Poissonian noise value 2eI, and that the noise approaches 1/3 of that value in superlattices whose quantum wells are strongly coupled. On the other hand, when the coupling is weak or when a strong electric field is applied to the superlattice, the noise becomes Poissonian. Although our results are qualitatively consistent with existing theories for one-dimensional multibarrier structures, the theories cannot account for the dependence of the noise on superlattice parameters that we have observed.     

Generating high harmonics in a superlattice based on graphene in the presence of static and alternating electric fields

The generation of high harmonics of current density in a superlattice based on graphene on a striped substrate is considered under the influence of static and alternating electric fields polarized along the superlattice axis. The areas of system parameter values are revealed for the first four harmonics, the amplitude of each of which surpasses the other three.     

Optical property and collective excitation of plasmon in a multiple-quantum-well superlattice in electric field

A finite type-I superlattice with different dielectric media on either side of the surfaces is considered under a perturbing electric fields parallel to the superlattice axis on the basis of an infinite square potential well. Using the random-phase approximation, the density–density correlation function including intra- and inter-level transitions in a multiple-quantum-well (MQW) is calculated. The dispersion relations for the surface and the bulk states are obtained as functions of the momentum wave vector and the averaged electric field strength over the quantum well. The Raman intensities due to the bulk and the surface plasmons for the intra- and the inter-level transitions are also obtained for incoming light energy.     

Current oscillation and chaotic dynamics in superlattices driven by crossed electric and magnetic fields

We have theoretically studied current oscillation and chaotic dynamics in doped GaAsAlAs superlattices driven by crossed electric and magnetic fields. When the superlattice system is driven by a dc voltage, a stationary or dynamic electric-field domain can be obtained. We carefully studied the electric-field-domain dynamics and current self-oscillation which both display different modes with the change of magnetic field. When an ac electric field is also applied to the superlattice, a typical nonlinear dynamic system is constructed with the ac amplitude, ac frequency, and magnetic field as the control parameters. Different nonlinear behaviors show up when we tune the control parameters.     

Intraband dynamics and terahertz emission in biased semiconductor superlattices coupled to double far-infrared pulses

This paper studies both the intraband polarization and terahertz emission of a semiconductor superlattice in combined dc and ac electric fields by using the superposition of two identical time delayed and phase shifted optical pulses. By adjusting the delay between these two optical pulses, our results show that the intraband polarization is sensitive to the time delay. The peak values appear again for the terahertz emission intensity due to the superposition of two optical pulses. The emission lines of terahertz blueshift and redshift in different ac electric fields and dynamic localization appears. The emission lines of THz only appear to blueshift when the biased superlattice is driven by a single optical pulse. Due to excitonic dynamic localization, the terahertz emission intensity decays with time in different dc and ac electric fields. These are features of this superlattice which distinguish it from a superlattice generated by a single optical pulse to drive it.     

Magnetotransport in a semconductor superlattice with transverse magnetic field

Magnetotransport in a semiconductor superlattice (SL) under transverse magnetic field has been investigated. It is shown that in weak magnetic and electric fields there is negative magnetoresistivity along the SL layers and positive magnetoresistivity along the SL axis. The Hall resistivity is much less than the usual semiconductor value. With an increase of electric field, there appears a negative differential conductivity (NDC) along the SL layers, and the Hall voltage depends nonlinearly on current density. In higher electric field, destroying the miniband structure, the magnetoresistivity along the SL axis is negative. The magnetoresistivity along the SL axis in strong magnetic field is positive for any current density. The Hall resistivity in strong magnetic (electric) field equals the classical value.     

电场中三层铁电超晶格的物理性质研究

基于微分算符技术的相关有效场理论研究用伊辛模型描述的铁电三层超晶格的物理性质。讨论了电场对电极矩、电极化率、热电系数等物理性质的影响。     

Wave packet dynamics in a semiconductor superlattice

We examine the time development of a wave packet in a superlattice miniband in a constant electric field, explicitly determining the time dependence of the probability density. Our analytic results permit the identification of breathing motion of the wave packet as well as Bloch oscillatory motion of its center-of-mass. The dynamical development of a Gaussian wave packet is exhibited, showing the appearance of images of the initial wave packet in nearby superlattice cells, exemplifying their participation in Bloch oscillatory and breathing motions.     

Dynamic conductivity of ac–dc-driven graphene superlattice

The dynamic conductivity of graphene superlattice in the presence of ac electric field and dc electric field with longitudinal and transversal components with respect to superlattice axis was calculated. In the case of strong transversal component of dc field conductivity of graphene superlattice was shown to be such as if the electrons had got the effective mass. In the case of weak transversal component of dc field conductivity was shown to change its sign if the frequency of ac field was an integer multiple of half of Bloch frequency.