V. 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.

Coulomb charging effects in an open quantum dot device

In this work we clarify the nature of frequent oscillations of the conductance of open quantum dots that were reported by Liang et al (Liang C-T et al 1998 Phys. Rev. Lett. 81 3507). Continuous and almost periodic oscillations superimposed upon ballistic conductance features are observed when the conductance G of the dot changes within a wide range 0 2e 2 /h is the consequence of suppression of inter-one-dimensional-subband scattering. The theory of Coulomb blockade and the Landauer formula are modified for the case of the quasi-one-dimensional system to describe combined charging and ballistic transport through the dot. Measured dependences of the conductance on the gate voltages and its temperature behaviour are correctly reproduced by the calculations.

Single-electron charging of triangular quantum dots in a ring interferometer

Small-size semiconductor ring interferometers operating in the Coulomb blockade regime have been experimentally and theoretically studied. The conductance as a function of the gate voltage exhibits narrow quasiperiodic peaks, which are further split into doublets. Based on the experimental structural data, a three-dimensional electrostatic potential, the energy spectrum, and the single-electron transport in the interferometer were modeled. The electron system can be divided into two triangular quantum dots connected by single-mode microcontacts to each other and to the reservoirs. A model of quantum dot charging in this system is proposed that explains the appearance of doublets in the conductance-gate voltage characteristics.

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.

The role of intersubband mixing in single-electron charging of open quantum dot

Abstract We compare the electrostatics and electron transmission through the quantum dots that have the inlet/outlet constrictions made by (i) split finger gates and (ii) overlaying finger gates. It has been found numerically that the intermode mixing is large in the former case while almost absent in the latter. We beleive this difference is responsible for single-electron charging of the open quantum dot of new type (ii) observed in C.-T. Liang et al. (Phys. Rev. Lett. 81 (1998) 3507). Our calculations show that the measured periods of conductance oscillations agree well with the change of the total charge of the dot by one elemental charge as the gate voltages change. Conventionally, single-electron charging does not show up in the transport through open quantum dots due to high transition probability from localized states to fully open channels.

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.