N. C. Mamani

Resonance oscillations of magnetoresistance in double quantum wells

We present the experimental and theoretical studies of the magnetoresistance oscillations induced by the resonance transitions of electrons between the tunnel-coupled states in double quantum wells. The suppression of these oscillations with increasing temperature is irrelevant to the thermal broadening of the Fermi distribution and reflects the temperature dependence of the quantum lifetime of electrons. The gate control of the period and amplitude of the oscillations is demonstrated.

Magnetoresistance oscillations in multilayer systems: Triple quantum wells

Magnetoresistance of two-dimensional electron systems with several occupied subbands oscillates owing to periodic modulation of the probability of intersubband transitions by the quantizing magnetic field. In addition to previous investigations of these magnetointersubband (MIS) oscillations in two-subband systems, we report on both experimental and theoretical studies of such a phenomenon in three-subband systems realized in triple quantum wells. We show that the presence of more than two subbands leads to a qualitatively different MIS oscillation picture, described as a superposition of several oscillating contributions. Under a continuous microwave irradiation, the magnetoresistance of triple-well systems exhibits an interference of MIS oscillations and microwave-induced resistance oscillations. The theory explaining these phenomena is presented in the general form, valid for an arbitrary number of subbands. A comparison of theory and experiment allows us to extract temperature dependence of quantum lifetime of electrons and to confirm the applicability of the inelastic mechanism of microwave photoresistance for the description of magnetotransport in multilayer systems.

Magnetotransport in AlxGax-1As Quantum Wells with Different Potential Shapes

We compare the transport properties for triangular, parabolic and cubic quantum wells. We calculate the transport mobility for electrons belonging to the different subbands. We obtain the energy spacing between first and second subbands from the electron sheet density and compare results for different potential profiles. We find that experimental results are in quantitative agreements with our calculations.

Nonlinear transport and oscillating magnetoresistance in double quantum wells

The nonlinear regime of low-temperature magnetoresistance of double quantum wells in the region of magnetic fields below 1 T is studied both experimentally and theoretically. The observed inversion of the magnetointersubband oscillation peaks with increasing electric current and splitting of these peaks are described by the theory based on the kinetic equation for the isotropic nonequilibrium part of electron distribution function. The inelastic-scattering time of electrons is determined from the current dependence of the inversion field.

Shubnikov-de Haas effect in tilted magnetic fields in wide quantum well

We study the magneto-resistance of a two-dimensional electron systems in a wide quantum well. We have considered two occupied subbands subjected to the tilted magnetic field in the regime of the magneto-inter-subband oscillations. We report on both experimental and theoretical studies of such a phenomenon and deduced information on the inter-subband energy gap in the presence of the in-plane magnetic field.

HALL RESISTANCE AND MANY-BODY EFFECTS IN A PARABOLIC WELL

We report on Hall effect measurements in 1000-4000 Awide AlxGax-1As parabolic wells with quasi-two-dimensional electrons and holes in the presence of a perpendicular magnetic field. Above a critical magnetic field B > 3T, the Hall resistance is found to increase when temperature decreases. We attribute such an enhanced Hall slope to the variation of the carrier density. The Hartree and exchange-correlation terms produce a strong variation of the potential well shap: the width of the electronic and hole slabs shrinks as magnetic field increases, which in turn leads to a charge redistribution between the well and impurity layer.