Alexander Olegovich Badrutdinov

The transport properties of an electronic Wigner solid (WS) on the surface of superfluid helium-4 are investigated in a geometry that allows WS systems of significantly different sizes to be defined. We probe and compare transport phenomena attributed to the electronic order, such as Bragg-Cherenkov scattering and the WS sliding transition, in the cases of a long homogeneous WS, a small WS island, and a long inhomogeneous WS. We find no significant WS size effects on the transport properties, in contrast to predictions of theoretical works, which indicates an absence of long-range order in the WS systems under consideration. For the inhomogeneous WS, consisting of two distinct WSs connected in series, a complex interplay of individual WS transport properties is observed, as revealed in the observation of two separate Bragg-Cherenkov plateaus and WS sliding transitions. A simple model is proposed that provides a qualitative explanation of this behavior.

The strong coupling regime is observed in a system of two-dimensional electrons whose cyclotron motion is coupled to an electromagnetic mode in a Fabry-Perot cavity resonator. Rabi splitting of eigenfrequencies of the coupled motion is observed both in the cavity reflection spectrum and ac current of the electrons, the latter probed by measuring their bolometric photoresponse. Despite the fact that similar observations of Rabi splitting in many-particle systems have been described as a quantum-mechanical effect, we show that the observed splitting can be explained completely by a model based on classical electrodynamics.

We report the first observation of an oscillatory photoconductivity response at the cyclotron-resonance harmonics in a nondegenerate 2D electron system formed on the free surface of liquid helium. The dc conductivity oscillations are detected for electrons occupying the ground surface subband. Their period is governed by the ratio of the microwave frequency to the cyclotron frequency. Theoretical analysis of the photoresponse in a strongly interacting electron system indicates that the observation can be explained by an oscillatory correction to the electron distribution function that appears for a large inelastic relaxation time because of photon-assisted scattering.

We investigate low-frequency collective excitations in a two-dimensional electron system on liquid helium-4 subject to high-frequency cyclotron resonant excitation in strong magnetic field. Under the cyclotron resonant excitation the frequency of the edge magnetoplasmon resonant mode shifts with respect to that in equilibrium. In addition, a novel collective excitation mode is observed. These findings are consistent with the conclusion of previous studies about the quasi-3D nature of the excited state of the system.

We report an experimental study of surface electrons on liquid helium-4 under cyclotron resonant excitation. Significant resonance-induced redistribution of electron density due to overheating was observed. Analysis of redistributed charges indicates an unusually large expansion of the electron system in a lateral direction, which cannot be understood in the framework of the generally accepted effective electron temperature approximation. To interpret the data we suggest that under resonant cyclotron pumping, a fraction of nonthermalized electrons is formed, in which the average energy associated with electron in-plane motion can significantly exceed the average energy associated with motion perpendicular to the helium surface.

We report an experimental investigation of energy relaxation of surface electrons on superfluid helium-4. Electrons are heated by resonant microwave radiation which excites electrons from the ground subband to the first excited subband. The conductivity of electrons is measured under applied microwave radiation and a change of conductivity due to the population of higher excited subbands is recorded. Experimental data are reproduced by numerical calculations, based on a theoretical model developed previously. Fitting calculated data to experimental data allows us to obtain information about energy relaxation of surface electrons. Our results support theoretical predictions for energy relaxation due to two-ripplon emission.

We report the observation of a peculiar charge stability diagram of a vertical double quantum dot, where the conventional Coulomb diamond edges have a sawtooth-like shape. This feature could be understood if we assume the formation of a third quantum dot in the semiconductor volume which is supposed to be a part of the source in the standard quantum dot measurement circuit. The size of this additional dot is larger compared to the size of the original ones, thus the charging energy is smaller, but it still exceeds the thermal energy and affects the electron transport through the structure. Since the big dot is coupled to small ones, the observed effect could be utilized for charge detection, which has always been a problem in the case of vertical quantum dots.

We report the observation of dynamic nuclear polarization in a vertical double quantum dot, as a result of a hyperfine interaction with three confined electrons. Our data allow us to distinguish three pumping regimes, characterized by different magnitudes and directions of polarization. Corresponding electron-nuclear spin dynamics is understood by considering relevant three-electron states mixed by hyperfine interaction. Also, an extremely long nuclear spin relaxation time is reported.

We study the spin splitting energies of different orbital states of quantum dots with a low-potential barrier. The experimental results show that the splitting energies are orbital state dependent. The theoretical analysis is done with a generalization of the Fock–Darwin states in the presence of spin–orbit interactions. The theoretical predictions match well with the experimental observations and exhibits that the Rashba interaction strength in vertical In_0.05Ga_0.95As/GaAs quantum dots is in the range 80≤λ_R≤120 meV Å. This enhanced Rashba spin–orbit interaction intensity can be understood from the high penetration of the electron wavefunction into the quantum well with a low-potential barrier.