O. A. Tkachenko

Aharonov-Bohm Oscillation Amplitude in Small Ballistic Interferometers

Small-radius (110 nm) ring interferometers were fabricated by the local anodic oxidation of AlGaAs/GaAs heterostructures containing 2D electron gas. Measurements and modeling show that a small ring asymmetry, which is detected by an atomic force microscope, leads to a small amplitude of Aharonov-Bohm oscillations, while a stronger asymmetry completely suppresses these oscillations.

Electrostatic Potential, Energy Spectrum, and Fano Resonances in a Ballistic Ring Interferometer Based on an AlGaAs/GaAs Heterojunction

For a ballistic ring interferometer based on high-mobility two-dimensional electron gas in an AlGaAs/GaAs heterojunction, the electrostatic potential and the energy spectrum are determined. It is shown that the splitting points in such an interferometer have the form of triangular potential wells. Calculation is performed for the two-dimensional electron transmission through the ring, and the Fano resonances caused by the coupling of the transmitted waves with the levels of higher transverse modes in triangular wells are predicted. These resonances are observed in the experiment.

Transformation of quantum size levels into virtual levels at the boundary between p-GaAs and an AlAs/GaAs superlattice

The transformation of quantum size levels into virtual levels upon a change in the electric field in an AlAs/GaAs superlattice located in the i region of a p-i-n structure is studied experimentally and theoretically. It is shown that an interfacial state at the boundary between the superlattice and the p-GaAs contact layer results in a resonant increase in the probability of photoelectron tunneling from the contact into the superlattice via Wannier-Stark levels.

Photon-assisted electron transport through a quantum point contact in a microwave field

It has been shown by the numerical solution of the time-dependent Schrödinger equation that the transmittance of an electron through a smooth one-dimensional barrier in a microwave field can increase by orders of magnitude in the tunneling regime and decrease strongly in the open regime. The leading contribution comes from transitions with absorption or emission of a few photons. The discovered effect can explain a recently observed strong increase in the conductance of a quantum point contact under microwave irradiation.

Introscopy of quantum nanoelectronic devices

Semiconductor nanoelectronic quantum devices are one of the achievements of contemporary physics and laboratory nanotechnologies. Short thin current channels are formed by electric fields in the plane of the two-dimensional electron gas deep below the surface of these devices. The real distribution of the electric fields and the picture of quantum transport in the channels can be reconstructed only by the combined experimental and numerical probing of the nanostructure. In this work, a concept of numerical introscopy, a method which is a natural continuation of the structural and electrophysical diagnostics and helps restore the picture of hidden processes and phenomena in nanostructures, is introduced on the basis of a few examples of the fabrication and investigation of nanodevices.

Ballistic Electron Wave Functions and Negative Magnetoresistance in a Small Ring Interferometer

By two-dimensional ballistic magnetotransport calculations, it is demonstrated that large-scale resistance peaks, typical of small ring interferometers in zero magnetic field, are suppressed at B∼1 T. This result is explained by the peculiarities of the interference pattern at the confluence sites of quantum wires and is in qualitative agreement with experimental data.

Coulomb blockade in a lateral triangular small quantum dot

An AlGaAs/GaAs lateral quantum dot of triangular shape with a characteristic size L<100 nm (the smallest size for dots of this type) containing less than ten electrons was studied theoretically and experimentally. Single-electron oscillations of the conductance G of this dot were measured at G<e2/h. When going from G≪e2/h to G≈0.5e2/h, a decrease was found not only in the amplitude but also in the period of oscillations. A calculation of the electrostatics demonstrated that this effect is due to a change in the dot size produced by control voltages.

Semiconductor artificial graphene: Effects in weak magnetic fields

Two-dimensional quantum transport through the stripe of the hexagonal lattice of antidots built in the multimode channel in the GaAs/AlGaAs structure has been studied numerically. It has been found that the low perpendicular magnetic fields (∼3 mT) suppress the bulk currents and cause the appearance of the edge Landau states and high positive magnetic resistance on both sides of the Dirac point. Tamm edge states are present in some energy intervals; as a result, the 4e2/h-amplitude oscillations caused by the quantization of these states on the lattice length are added to the steps of the conductance quantization Gn = (2|n| + 1)2e2/h.

Temperature dependence of conductance and thermopower anomalies of quantum point contacts

It has been shown within the Landauer approach that the presence of the 0.7 anomaly in the conductance of a ballistic microcontact and the respective plateau in the thermopower implies pinning of the potential barrier height at a depth of kBT below the Fermi level. A simple way of taking into account the effect of electron-electron interaction on the profile and temperature dependence of a smooth one-dimensional potential barrier in the lower subband of the microcontact has been proposed. The calculated temperature dependences of the conductance and Seebeck coefficient agree with the experimental gate-voltage dependences, including the emergence of anomalous plateaus with an increase in temperature.

Coherent Scattering in a Small Quantum Dot

Ballistic transport in an open small (100 nm) three-terminal quantum dot has been analyzed. The dot is based on the high-mobility 2D electron gas of the AlGaAs/GaAs heterojunction. It has been shown that the gate oscillations of the resistance of such a dot arise due to the coherent scattering of electrons on its quasidiscrete levels and these oscillations are suppressed by a weak magnetic field.