Spin-polarized two-dimensional electron gas at oxide interfaces

The possibility of formation of a fully spin-polarized 2D electron gas at the SrMnO_3/(LaMnO_3)_1/SrMnO_3 heterostructure is predicted from density-functional calculations. The La(d) electrons become confined in the direction normal to the interface in the electrostatic potential well of the positively charged layer of La atoms, acting as electron donors. These electrons mediate a ferromagnetic alignment of the Mn t_2g spins near the interface via Zener double exchange and become, in turn, spin-polarized due to the internal magnetic fields of the Mn moments.     

High-quality two-dimensional electron gas at large scale GaN/AlGaN wafer interface prepared by mass production MOCVD systems

Basic electronic properties of two-dimensional electron gas (2DEG) formed at GaN/AlGaN hetero-interface in large-scale (100 mm) wafer made by metal organic chemical vapour deposition (MOCVD) have been reported and discussed. From conventional Hall measurements, highest electron mobility was found to be μ_e∼1680 and 9000 cm²/V s at room temperature and at ∼5 K, respectively, for sheet electron density of n_s∼8×10¹² cm⁻². In magneto-resistance (MR) measurements carried out at 1.5 K in Hall bar sample defined by photolithography and ion implantation, very clear Schubnikov de-Haas oscillations and integer quantum Hall effect were observed in diagonal (R_xx) and off-diagonal (R_xy) resistances, respectively. In addition, a good insulating nature of GaN layer is confirmed by capacitance-voltage (C-V) measurement. These results suggest the high-qualitiness of our 100 mm GaN/AlGaN high electron mobility transistor (HEMT) wafers comparable to those so far reported.     

Quantum mechanical Monte Carlo approach to electron transport at heterointerface

With the progress of LSI technology, the electronic device size is scaled down to the sub 0.1μ m region. In such an ultrasmall device, it is indispensable to take quantum mechanical effects into account in device modeling. In this paper, we present a newly developed quantum Monte Carlo device simulation applicable to ultrasmall semiconductor devices. In this model, the quantum effects are represented in terms of quantum mechanically corrected potential in the classical Boltzmann equation. It is demonstrated that the quantum transport effects such as tunneling and energy quantization in ultrasmall semiconductor devices are obtained for the first time by using the standard Monte Carlo techniques.     

Prediction of high-mobility two-dimensional electron gas at KTaO_3-based heterointerfaces

First-principles calculations are performed to explore the possibility of generating the two-dimensional electron gas(2 DEG) at the interface between LaGaO_3/KTaO_3 and NdGaO_3/KTaO_3(001) heterostructures. Two different models —i.e., the superlattice model and the thin film model — are used to conduct a comprehensive investigation of the origin of charge carriers. For the symmetric superlattice model, the LaGaO_3(or NdGaO_3) film is nonpolar. The 2 DEG with carrier density on the order of 1014 cm~(-2) originates from the Ta dxy electrons contributed by both LaGaO_3(or NdGaO_3) and KTaO_3. For the thin film model, large polar distortions occur in the LaGaO_3 and NdGaO_3 layer, which entirely screens the built-in electric field and prevents electrons from transferring to the interface. Electrons of KTaO_3 are accumulated at the interface, contributing to the formation of the 2 DEG. All the heterostructures exhibit conducting properties regardless of the film thickness. Compared with the Ti dxy electrons in SrTiO_3-based heterostructures, the Ta dxy electrons have small effective mass and they are expected to move with higher mobility along the interface. These findings reveal the promising applications of 2 DEG in novel nanoelectronic devices.     

Oscillatory magnetization of two-dimensional electron gas

Diamagnetic moment of the two-dimensional electron gas is calculated for finite temperature using a simple energy band model and assuming no collisional broadening of Landau levels. Numerical results are presented for GaAs band parameters. The diamagnetic moment oscillates around zero value as a function of magnetic field strength and tends to zero at low fields. It is concluded that both the diamagnetic and the paramagnetic susceptibilities of the 2D electron gas vanish in the low field limit.     

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.     

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.     

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.     

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.     

The spin-double refraction in two-dimensional electron gas

We briefly review the phenomenon of the spin-double refraction that originates at an interface separating a two-dimensional electron gas with Rashba spin–orbit coupling from a one without. We demonstrate how this phenomenon in semiconductor heterostructures can produce and control a spin-polarized current without ferromagnetic leads.     

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).

     

Observation of an interedge magnetoplasmon mode in a degenerate two-dimensional electron gas

We study the propagation of edge magnetoplasmons by time-resolved current measurements in a sample which allows for selective detection of edge states in the quantum Hall regime. At filling factors close to nu=3 we observe two decoupled modes of edge excitations, one of which is related to the innermost compressible strip and is identified as an interedge magnetoplasmon mode. From the analysis of the propagation velocities of each mode the internal spatial parameters of the edge structure are derived.     

Many-body effects in spin-polarized two-dimensional electron gas

Many-body effects on the spin polarization are studied in an n channel inversion layer on Si (1 0 0) surface in a magnetic field parallel to the surface in random phase approximation. The spin polarization exhibits a discrete jump to a full polarization at the critical magnetic field in the low-density regime and the critical field is reduced considerably from that estimated by an extrapolation based on the zero-field susceptibility.     

Spin-plasmon oscillations of the two-dimensional electron gas

Interaction of the spins of 2D electrons with an alternating electric field in the plane of the system is considered. It is assumed that the double spin degeneracy is eliminated by the spin-orbit splitting. It is shown that transitions between different spin states produce a narrow absorption band in the degenerate electron gas. In the frequency domain corresponding to these transitions, those frequencies are combined with two-dimensional plasmons; as a result, the plasmon spectrum is modified, and a new type of oscillations occurs, namely, a spin-plasmon polariton. The dispersion law of these oscillations is derived. The problem of the excitation of spin-plasmon polaritons by an external electromagnetic field is solved.