N.T. Moshegov

2D lattice of coupled Sinai billiards: metal or insulator at g ≪ 1?

We investigate the transport in a two-dimensional (2D) lattice of coupled Sinai billiards fabricated on the basis of a high-mobility 2D electron gas in a GaAs/AlGaAs heterojunction in going from g >1t o g1 (where ga r/(e 2 /h )i s dimensionless conductivity). The data obtained suggest that the system studied behaves more like a metal than an insulator at g 1 and is not described by the generally accepted picture of metal‐insulator transition in 2D electron systems. ” 1998 Published by Elsevier Science B.V. All rights reserved.

Landau levels in two and three-dimensional electron gases in a wide parabolic quantum well

Shubnikov-de Haas oscillations are measured in a wide parabolic quantum well with 6 subbands in a tilted magnetic fi eld. We find two types of oscillations. The oscillations at low magnetic field are shifted towards higher fields with tilted angles, and can be attributed to the two-dimensional Landau state at the bottom subband. The position of the second type oscillations do not shift with tilted angles indicating a three-dimensional character of the Landau state formed by the highest subbands. The bottom level in the quantum well is not overlapped with the highest subbands due to the enhanced quantum scattering time of the lowest subbands.

Commensurability oscillations in wide parabolic well in the presence of an in-plane magnetic field

Abstract The commensurability oscillations in antidot lattices with different periods are studied in the tilted magnetic field in wide parabolic quantum well with five occupied subbands. We find that the commensurability peaks are continuously transformed to new magnetoresistance oscillations, when magnetic field is directed parallel to the well plane. The positions of the new peaks correspond to R c / W e ≈2.3 and 1, where R c is the cyclotron radius, and W e is the quantum well width. This result is consistent with recent quantum-mechanical calculations of the magnetoresistance in the presence of boundary-roughness scattering.

Shubnikov-de Haas oscillations in a nonplanar two-dimensional electron gas

We have measured the Shubnikov-de Haas (SdH) oscillations of a nonplanar two-dimensional electron gas (2DEG) fabricated by overgrowth of a GaAs/AlGaAs heterojunction on a pre-patterned substrate. When placed in a uniform external magnetic field B, the field normal to the nonplanar 2DEG is spatially modulated, and electrons experience a nonuniform magnetic field. In a tilted magnetic field, the SdH oscillations are much more strongly damped than in a field perpendicular to the substrate. We consider several mechanisms which may be responsible for the anomalous behaviour of the SdH oscillations in the tilted magnetic field. We conclude that the electron scattering by the magnetic field spatial fluctuations plays a main role in the transport properties of a nonplanar 2DEG at low magnetic field. An analysis of the Shubnikov-de Haas oscillations in a tilted magnetic field provides a new method to study the surface profile of a nonplanar heterostructure containing a 2DEG.

Universal conductance fluctuations in a two-dimensional electron gas near filling factor v=12

Abstract We report magnetoresistance measurements on a two-dimensional electron gas at low magnetic field and near Landau filling factor v = 1 2 in mesoscopic samples. Aperiodic reproducible resistance fluctuations have been found in both cases. In order to show that the fluctuations in a strong field are due to the quantum interference of the composite Fermions, we have compared coherence properties for the electrons and composite particles.

Magnetooscillations of electrons in nonparabolic confining potential

Abstract Shubnikov–de Haas (SdH) oscillations induced by the small additional perpendicular field are investigated in overfilled parabolic quantum well in the presence of the parallel magnetic field. The dispersion relation of the in-plane electron motion has a double minimum in contrast to the harmonic-oscillator model. Landau levels belonging to the additional subband minima are responsible for the observed behaviour of the SdH oscillations.

Quantum hall effect in a wide parabolic quantum well

We investigate the activated conductivity for Landau levels at lling factors v =1,2 in a parabolic AlxGa1-x As well down to 30 mK. We obtain a very small activation energy ~ 0.02 meV, which is almost 1-2 orders of magnitude smaller than the expected values for energy gaps in a wide quantum well. The resistivity minima vanish completely when a parallel component of magnetic field is applied. The collapse of the energy gaps in the wide parabolic well occurs due to the new electron correlated state, probably the charge density wave state predicted for a uniform wide electron slab in high magnetic field.

Coherence properties of submicron GaAs/AlGaAs rings with a ferromagnetic gate

Abstract In the present work, the Aharonov–Bohm effect in submicron GaAs/AlGaAs ring with an in-plane ferromagnetic gate is investigated. The experiment is based on the study of the derivatives of magnetoresistance and microwave EMF to gate voltage. The experimental results are explained by electron wave interference in the presence of an inhomogeneous magnetic field in the ring.

Magnetooscillations in a wide parabolic well in the presence of an in-plane magnetic field

Abstract The magnetoresistance oscillations in a wide parabolic quantum well are investigated at low temperatures in a tilted magnetic field. Magnetooscillations in the presence on an in-plane magnetic field cannot be explained by the diamagnetic Shubnikov–de Haas (Sd H) effect. Three-dimensional character of the electron motion can be responsible for this behaviour.