High-frequency conductivity of a two-dimensional electron gas with impurity electron states

The high-frequency conductivity tensor for a two-dimensional electron gas with short-range-acting impurity atoms has been computed. Spatial dispersion of the conductivity was taken into account. The threshold and maxima of the dissipative part of the conductivity arising from ionization of the impurity atoms by the field of electromagnetic waves were found. Numerical calculations of the conductivity were carried out for semiconductor structures with a two-dimensional electron gas. Khar’kov State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 91–94, July, 1997.     

Magnetic bloch electron states and spin polarization in 2D superlattices without an inversion center with Rashba spin-orbit interaction in an electron gas

The quantum states of carriers in 2D doubly periodic n-type semiconducting superlattices without spatial inversion symmetry in an external magnetic field are calculated in the one-electron approximation. It is shown that the spin-orbit interaction and spin splitting in the magnetic field may lead to the occurrence of the photovoltaic effect in a 2D electron gas without an inversion center and to a nonzero spin magnetization of the electron gas in the plane perpendicular to the magnetic field.     

Minigap plasmons in a two-dimensional electron gas subjected to a one-dimensional periodic potential

We investigate the plasmon excitations in a two-dimensional electron gas subjected to a one-dimensional weak periodic potential. We derive and discuss the dispersion relations for both intrasubband and intersubband excitations within the framework of Bohm-Pines' random-phase approximation. For such an anisotropic system with spatially modulated charge density, we observe a splitting of the 2D plasmon dispersion. The splitting is caused by the superlattice effect of the charge-density modulation on the collective excitation spectrum. We also discuss how the tunneling and the potential amplitude affect the plasmon excitations.     

The microwave Hall effect of a two-dimensional electron gas

The integer Quantum Hall effect has been recently observed in the Hall conductivity _xy at microwave frequencies. Here we present a calculation of the wave propagation in the crossed waveguide system used in the experiments. The field pattern is more complicated than in the case of a pure plane wave. The essential result, however, remains unchanged: The field strength in the second (crossed) waveguide is proportional to _xy of the two-dimensional electron gas. Dedicated to Professor Karlheinz Seeger on the occasion of his 60th birthday     

Magnetic ratchet effects in a two-dimensional electron gas

The effect of the magnetic field on the generation of an electric current in a two-dimensional electronic ratchet is theoretically studied. Mechanisms of the formation of magnetically induced photocurrent are proposed for a structure with a two-dimensional electron gas (quantum well, graphene, or topological insulator) with a lateral asymmetric superlattice consisting of metallic strips on the external surface of the structure. The ratchet with the spatially oscillating magnetic field generated by the ferromagnetic lattice, as well as the nonmagnetic ratchet placed in the uniform magnetic field both classically weak and strong quantizing, is considered. It is established that the ratio of the amplitude of the magnetic oscillations of photocurrent to the ratchet photocurrent in zero field can exceed two orders of magnitude.     

Magnetoplasma modes of a spatially periodic two-dimensional electron gas

We examine the magnetoplasma dispersion of a two-dimensional electron gas with a spatially periodic charge density. The system studied is a periodic array of two-dimensional electron gas strips with constant equilibrium density. The integral equation describing the charge fluctuations on the strips, has been derived and solved numerically. The spatial dependence of the form of either propagating or evanescent waves. The latter are associated with the edge modes, recently discovered in electrons on liquid⁴ He. For a periodic array of two-dimensional strips, the modes in different strips, interact and form bands.     

Zero differential resistance of a two-dimensional electron gas in a one-dimensional periodic potential at high filling factors

The nonlinear magnetotransport of a two-dimensional (2D) electron gas in one-dimensional lateral superlattices based on a selectively doped GaAs/AlAs heterostructure is studied. The one-dimensional potential modulation of the 2D electron gas is performed by means of a series of metallic strips formed on the surface of a heterostructure with the use of electron beam lithography and a lift-off process. The dependence of the differential resistance r_xx on the magnetic field B < 1.5T in superlattices with the period a = 400 nm at a temperature of T = 4.2 K is investigated. It is found that electronic states with r_xx ≈ 0 appear in one-dimensional lateral superlattices in crossed electric and magnetic fields. It is shown that states with r_xx ≈ 0 in 2D electronic systems with one-dimensional periodic modulation arise at the minima of commensurability oscillations of the magnetoresistance.     

Nonlinear effects in a two-dimensional electron gas with a periodic lattice of scatterers

The magnetoresistance of two-dimensional (2D) electrons in a periodic lattice of antidots is found to be substantially influenced by an applied electric field. The non-Ohmic behavior of the resistance in the region of commensurability oscillations originates from the electric-field-induced breakdown of the trajectories skipping along the lattice arrays. In the region of magnetic fields where the cyclotron diameter is less than the distance between antidots the breakdown of the orbits skipping around antidots is responsible for the nonlinear behavior of the magnetoresistance. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 3, 237–241 (10 February 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Nonlocal effects in a two-dimensional electron gas with a periodic lattice of scatterers

The nonlocal resistance of a two-dimensional electron gas in a periodic lattice of antidots is investigated. Anomalous growth of this resistance is observed when 2R _c ≈d (R _c is the Larmor radius). This growth is caused by the appearance of runaway trajectories, skipping along the antidots and running away along the rows of antidots. It is shown on the basis of a comparative analysis of the local and nonlocal magnetoresistance that the character of the electronic billiard trajectories corresponds to the characteristic features of magnetotransport. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 336–341 (10 March 1996)     

Magnetic moment of a two-dimensional degenerate electron gas in mesoscopic samples

The orbital magnetism of two-dimensional electrons in mesoscopic samples is studied in models where the interaction between electrons is neglected. Various geometries are considered as there are disc, plaquette, bracelet with hard wall confinement and also a confinement with a parabolic potential. We calculate the average magnetic moment which means an average with respect to size fluctuations and de Haas-van Alphen oscillations which arise in the case of a sharp Fermi cutoff. We see three distinct ranges in the magnetic field: (i) small field region where perturbation theory applies; (ii) moderate fields where edge currents play a prominent role; and (iii) the high field range with a Landau type susceptibility. In a quasiclassical picture, the electronic orbits are not qualitatively changed by a magnetic field in (i); skipping orbits are important in (ii); and in (iii), the cyclotron radius is smaller than the sample size. As a rule, we find an enhancement of the magnetic response which increases with k_FL, that is, with sample size divided by the Fermi wave length. Also, we have found out that the quasiclassical approximation fails in the calculation of the magnetic properties; on the other hand, we have seen no essential differences between the canonical ensemble (fixed particle number) and the grand canonical ensemble (chemical potential given). In the case of plaquettes, in particular for samples in the form of squares, we have found agreement with experimental results by Lévy, Reich, Pfeiffer and West.     

Anomalous Hall effect in a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interaction

We discuss the mechanism of the anomalous Hall effect in a Rashba-Dresselhaus two-dimensional electron gas subjected to a homogeneous out-of-plane magnetization. On the basis of a systematic treatment of the kinetic equations for the spin-density matrix, results are derived for the dynamic Hall conductivity in a closed form. Its nonanalytic dependence on both the scattering time and the frequency of the applied electric field is discussed. Except for in a special Rashba-Dresselhaus model, there is a finite intrinsic anomalous Hall effect, which is extremely sensitive to short-range elastic scattering.     

Realization of a spin-polarized two-dimensional electron gas via image-potential-induced surface states

Electrons in image-potential-induced surface states form a two-dimensional electron gas in front of the surfaces. In the case of ferromagnets, their binding energies as well as lifetimes depend on the orientation of their spin magnetic moment with respect to the magnetization direction. Various experiments with inverse photoemission and two-photon photoemission to detect the spin dependence of image states are reviewed. A new and successful approach to achieve and detect a spin-polarized two-dimensional electron gas is presented, namely polarization-dependent and spin-resolved two-photon photoemission. Additional time resolution opens the way to study spin-dependent electron dynamics.     

Dynamical response properties of a two-dimensional electron gas in a weak periodic magnetic modulation

Calculating the dynamical dielectric response function for a two-dimensional electron gas (2D EG) under a perpendicular magnetic field and subjected to an additional weak unidirectional periodic magnetic field within the random-phase approximation (RPA), we find that not only is the response function broadened in the presence of the magnetic modulation, but it is also found to contain a series of subsingularities at the band edges which are attributed to the magnetic modulation induced broadening of the energy spectrum.