Solitons in a two-dimensional electron gas

The non-linear spectrum of a two-dimensional electron gas (2-DEG) formed at the interface of a heterostructure is investigated. This spectrum is found to contain a new type of localized excitation exhibiting soliton behavior. A matrix formulation of the model equations permits the extraction of the equation of evolution in space for these excitations. Results are presented for the boundary value problem excited by temporal Gaussian pulses.     

Magnetotransport in a modulated two-dimensional electron gas

We propose a semiclassical theory of dc magnetotransport in a two-dimensional electron gas modulated along one direction with weak electrostatic modulations. We show that oscillations of the magnetoresistivity ρ_∥ corresponding to the current driven along the modulation lines observed at moderately low magnetic fields can be explained as commensurability oscillations.     

Commensurability oscillations in a stripe-shaped two-dimensional electron gas

We have studied the commensurability oscillations for a nonplanar, two-dimensional electron gas which is confined to a surface spatially modulated both in the transverse and longitudinal directions. We show, numerically, that coupling the drift in both directions causes the motion to be chaotic. The channeling tori, responsible for conduction along the stripes, are destroyed and the averaged squared drift velocities decrease.     

Spin-dependent transport in a magnetic two-dimensional electron gas

Magneto-transport and magneto-optical probes are used to interrogate spin-dependent transport in magnetic heterostructures wherein a two dimensional electron gas (2DEG) is exchange-coupled to local moments. At low temperatures, the significant s–d exchange-enhanced spin splitting in these “magnetic” 2DEGs is responsible for the observation of unusual transport properties such as a complete spin polarization of the gas at large Landau level filling factors and a pronounced, non-monotonic background magneto-resistance. Magneto-transport measurements of gated samples performed in a parallel field geometry are used to systematically study the variation of the magneto-resistance with sheet concentration, yielding new insights into the dependence of spin transport on the Fermi energy of the majority spin carriers.     

Nondiffusive spin dynamics in a two-dimensional electron gas

We describe measurements of spin dynamics in the two-dimensional electron gas in GaAs/GaAlAs quantum wells. Optical techniques, including transient spin-grating spectroscopy, are used to probe the relaxation rates of spin polarization waves in the wave vector range from zero to 6x10(4) cm-1. We find that the spin polarization lifetime is maximal at a nonzero wave vector, in contrast with expectations based on ordinary spin diffusion, but in quantitative agreement with recent theories that treat diffusion in the presence of spin-orbit coupling.     

Quantum magnetotransport in a modulated two-dimensional electron gas

Quantum mechanical calculations of the magnetotransport coefficients of a modulated two-dimensional electron gas in a perpendicular magnetic field are presented using the Kubo method. The model modulation potential used is such that the effect of the steepness of the potential and its strength on the band part of the longitudinal resistivity ρ_xxand the Hall resistivity ρ_xycould be studied. In the extreme limit of a very steep potential, a two-dimensional square array of antidots is simulated. Impurity scattering is included in the self-consistent t-matrix approximation. The results show that for a strong lateral superlattice potential, ρ_xyis quenched in the low magnetic field regime and as the magnetic field increases there is a large negative Hall resistivity. The intensity of this negative peak is suppressed as the strength of the modulation potential is decreased. It is also shown that the height of the negative peak depends on the steepness of the potential. The longitudinal resistivity also has some interesting features. There are Aharonov–Bohm oscillations and a double peak structure which depends on both the strength of the modulation potential as well as its slope. The numerical results show that the position and intensity of the lower peak is not very sensitive to a change in the strength of the lattice potential or its steepness. However, the upper peak is greatly reduced when the lattice potential is diminished in strength. The double peak feature in ρ_xxand the negative peak and quenching of the Hall effect at low magnetic fields have been observed experimentally for antidots in both the quasiclassical and quantum regimes.     

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.     

Spatial correlations of a two-dimensional electron gas

The pair distribution function of a two-dimensional degenerate electron gas is evaluated in the chain diagram approximation and its asymptotic behavior is investigated. It shows characteristic oscillations at large distances. A sum rule of the eigenvalues of the free particle propagator is obtained. It can be used for the evaluation of the exchange energy and other purposes.This work was supported by the National Science Foundation.     

Magneto-excitations in the rotating two-dimensional electron gas

Summary The effects of a rigid rotation on the two-dimensional electron gas are studied. For very large wavelengths the lower branch of magneto-excitations has the dispersion relationE_(k)≈[ℏΓ (ℏΓ+ve ²|k|)]^1/2 , wherev is the filling factor and Γ the angular speed of rotation. The result holds independently of the presence of a solid phase (Wigner lattice) on the gas.

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Riassunto Si studiano gli effetti di una rotazione rigida su un gas di elettroni bidimensionale. Per lunghezze d'onda molto ampie, il ramo piú basso delle eccitazioni magnetiche ha la relazione di dispersioneE_(k)≈[ℏΓ (ℏΓ+ve ²|k|)]^1/2 dovev è il fattore di riempimento e Γ la velocità angolare di rotazione. Il risultato vale indipendentemente dalla presenza di una fase solida (reticolo di Wigner) nel gas.

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Резюме Исследуется влияние жесткого вращения на двумерный электронный газ. Для очень больших длин волн низшая ветвь магнитных возбуждений имеет дисперсионное соотношениеE_(k)≈[ℏΓ (ℏΓ+ve ²|k|)]^1/2, гдеv-фактор заполнения и Γ-угловая скорость врашения. Полученный результат оказывается справедлив в присутствии твердой фазы (решетка Вигнера).

     

Quantum oscillations in screening in a two-dimensional electron gas

The static dielectric constant of a two-dimensional electron gas is studied as a function of the strength of a dc magnetic field applied normal to the plane of the electron gas. At high temperatures $\text{(kT ?}\text{h}\text{?}\text{ω}{}_{\mathrm{c}}\text{)}$ the static dielectric function is independent of magnetic field, and for long wavelengths is given by ? ? ?₀ + 2n_vme²/q, where ?₀ is the background dielectric constant and n_v is the valley degeneracy. At low-temperatures, quantum oscillations become important and dramatically modify the screening.     

Screening effects in two-dimensional electron gas

The potential produced by a charged impurity at the interface of a highly doped GaAlAs and GaAs is calculated at a finite temperature. The electron gas formed at the interface is described as a two dimensional gas in which the impurity is assumed to be dipped. Temperature dependence of the impurity potential is calculated in the random phase approximation (R.P.A.) as well as in the modified temperature dependent Thomas-Fermi (M.T.T.F.) approximation which is defined to include temperature effects and to reduce to Thomas-Fermi result at zero temperature. The binding energy of the impurity for the ground state is calculated in R.P.A. and in M.T.T.F.. It is shown that at temperature T, much larger than the Fermi temperature, T_F, M.T.T.F. gives binding energies close to R.P.A. results.