Lateral Semiconductor Superlattice Research Articles

Asymmetric Landau bands due to spin–orbit coupling

We show that the Landau bands obtained in a two-dimensional lateral semiconductor superlattice with spin–orbit coupling (SOC) of the Rashba/Dresselhaus type, linear in the electron momentum, placed in a tilted magnetic field, do not follow the symmetry of the spatial modulation. Moreover, this phenomenology is found to depend on the relative tilt of magnetic field and on the SOC type: (a) when only Rashba SOC exists and the magnetic field is tilted in the direction of the superlattice (b) Dresselhaus SOC exists and the magnetic field is tilted in the direction perpendicular to the superlattice. Consequently, measurable properties of the modulated system become anisotropic in a tilted magnetic field when the field is conically rotated around the z axis, at a fixed polar angle, as we demonstrate by calculating the resistivity and the magnetization.

BEATS OF THE MAGNETOCAPACITANCE OSCILLATIONS IN LATERAL SEMICONDUCTOR SUPERLATTICES

We present calculations on the magnetocapacitance of the two-dimensional electron gas in a lateral semiconductor superlattice under two-dimensional weak periodic potential modulation in the presence of a perpendicular magnetic field. Adopting a Gaussian broadening of magnetic-field-dependent width in the density of states, we present explicit and simple expressions for the magnetocapacitance, valid for the relevant weak magnetic fields and modulation strengths. As the modulation strength in both directions increase, beats of the magnetocapacitance oscillations are observed, in the low magnetic field range (Weiss-oscillations regime), which are absent in the one-dimensional weak modulation case.

Generation of unipolar pulses during interaction between electromagnetic radiation and a lateral semiconductor superlattice

We theoretically predict the effect of generation of unipolar electromagnetic pulses during interaction between intense terahertz electromagnetic radiation and quantum lateral semiconductor superlattices. It is shown that this effect takes place when a superlattice is irradiated by pulsed signals and is due to the fact that stability of the limit cycles describing the dynamic behavior of the system changes successively with the variation in the external-field amplitude. It is noted that such an effect should also be expected in the response of a low-capacitance Josephson junction to a quasiharmonic forcing.

Theory of electronic light scattering in lateral superlattices with Rashba spin–orbit coupling under quantizing electric and magnetic fields

The influence of an in-plane electric and out-of-plane magnetic field on the electronic light scattering is calculated for a lateral semiconductor superlattice within Rashba spin–orbit interaction. Sharp resonances are predicted to appear when the Raman shift matches one frequency of the Wannier–Stark ladder. The spin–orbit interaction gives rise to a dispersion of the exact one-particle eigenstates and an associated finite width of the Raman line, which can be tuned by the electric and magnetic field. When the Bloch frequency is located in this Raman line, a Fano resonance is observed.

Spin accumulation in lateral semiconductor superlattices induced by a constant electric field

The electric-field dependence of the spin accumulation in strongly coupled lateral superlattices subject to Rashba spin-orbit interaction is studied by the density-matrix approach. At low fields, the spin accumulation depends linearly on the electric field. In this field regime, the magnitude of the homogeneous magnetization is larger in the lateral superlattice than in the corresponding two-dimensional electron gas. The magnetization exhibits a maximum as a function of the electric field. In the region of Wannier-Stark localization, the field-induced magnetization decreases with increasing electric field strength. Field-mediated resonant-tunneling transitions between different spin states manifest themselves in a spin depolarization.

Current-induced spin accumulation in lateral superlattices with Rashba and Dresselhaus spin–orbit interaction

The current-induced spin accumulation is calculated for a 1D lateral semiconductor superlattice with spin–orbit interaction of the Rashba and Dresselhaus type. Due to its particular symmetry, the Rashba interaction alone only leads to an in-plane component of the magnetization transverse to the applied electric field. When in addition a Dresselhaus contribution is present, this symmetry is lifted, and all components of the magnetization are induced by the electric field. Based on the density-matrix approach, the induced spin polarization is determined as a function of external in-plane electric and magnetic fields.

Excitation of Bloch oscillations in a lateral semiconductor superlattice under the influence of electromagnetic pulses

The conversion of the carrier frequency of electromagnetic pulses in lateral semiconductor superlattices, associated with the excitation of Bloch oscillations in the superlattice, is studied theoretically. Conditions are found that are necessary for the observation of the radiation of a Bloch oscillator. The energy characteristics of the efficiency of frequency multiplication and the spectral distribution of the radiation transmitted through the superlattice are calculated. It is shown that low-frequency collisions of electrons do not suppress the excitation of Bloch oscillations, which can be observed under the interaction of the superlattice not only with a pulsed, but also with a continuous-wave signal.

Terahertz radiation of Bloch oscillators excited by an electromagnetic field in lateral semiconductor superlattices

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.

Lateral superlattices in a strong electromagnetic field: Self-induced transparency, multistability, and frequency multiplication

Self-action and generation of the harmonics of intense electromagnetic radiation interacting with quantum lateral semiconductor superlattices are investigated theoretically using a self-consistent approach. The calculations are based on a semiclassical description of electron transport in a conduction miniband in an electrodynamic model of an equivalent current screen. Multistep, multistable, self-induced transparency is obtained. The effect is associated with the dynamic localization of electrons in the self-consistent electromagnetic field and it appears only if the density of free current carriers in the superlattice is higher than a certain critical value. It is shown that the bleaching of the structure is accompanied by efficient generation of odd-numbered radiation harmonics, whose intensity peaks lie near the transparency threshold.

Hot-electron magneto-miniband transport in lateral semiconductor superlattices

We present a theoretical analysis of hot-electron magneto-miniband transport in a lateral semiconductor superlattice. Our approach is based on the recently developed balance-equation theory extended to the lateral superlattice in the presence of crossed magnetic and electric fields. Realistic scatterings due to impurities, acoustic phonons and polar optic phonons are taken into account in the study. Negative differential velocities appear at high electric field for all the directions in the superlattice plane, but the linear mobility and the peak drift velocity in the (10)-direction are higher than those in the (11)-direction. Special attention is paid to the perpendicular (Hall) conduction. The magnitude and the sign of the Hall resistivity in linear and non-linear transport not only varies strongly with the carrier density but also varies with the electron temperature.

Theory of weak localization in a lateral superlattice

A theory of weak localization for the parallel and transverse conductivity in lateral semiconductor superlattices is presented. Based on our previous studies of planar superlattices, we assume that there exists coherent transport between quantum wires. The theory explicitly accounts for the superlattice periodic structure. Small collisional broadening calculations are performed as quantum corrections to Boltzmann transport. Similar to planar superlattices, weak localization corrections to the conductivity depend on the width of the superlattice miniband. This theory allows for (i) direct determination of the effective interwire electron coupling by measurement of the parallel conductivity, and (ii) computation of the electron dephasing time (such as the electron-electron scattering time) for this quantum structure.