arXiv subjects
Publications and source records attributed to A. A. Bykov.
The lifetime of two dimensional electrons in GaAs quantum wells, placed in weak quantizing magnetic fields, is measured using a simple transport method in broad range of temperatures from 0.3 K to 20 K. The temperature variations of the electron lifetime are found to be in good agreement with conventional theory of electron-electron scattering in 2D systems.
Microwave induced photoconductivity of a two-dimensional electron gas (2DEG) in selectively-doped GaAs/AlAs heterostructures has been studied using the Corbino geometry with capacitive contacts at a temperature T=1.6K and magnetic field B up to 0.5 T. Zero-conductance states have been observed in the samples under study subject to microwave radiation, similarly to the samples with ohmic contacts. It has been shown that ohmic contacts do not play a significant role for observation of zero-conductance states induced by microwave radiation
The temperature dependence of phonon-induced resistance oscillations has been investigated in two-dimensional electron system with moderate mobility at large filling factors at temperature range T = 7.4 - 25.4 K. The amplitude of phonon-induced oscillations has been found to be governed by quantum relaxation time which is determined by electron-electron interaction effects. This is in agreement with results recently obtained in ultra-high mobility two-dimensional electron system with low electron density [A. T. Hatke et al., Phys. Rev. Lett. 102, 086808 (2009)]. The shift of the main maximum of the magnetophonon resistance oscillations to higher magnetic fields with increasing temperature is observed.
Low-temperature electron magnetotransport in single GaAs quantum wells with two populated subbands is studied at large filling factors. Magneto-inter-subband (MIS) and acoustic-phonon induced oscillations of the dissipative resistance are found to be coexisting but interfering substantially with each other. The experiments show that amplitude of the MIS-oscillations enhances significantly by phonons, indicating "constructive interference" between the phonon scattering and the intersubband electron transitions. Temperature damping of the quantum oscillations is found to be related to broadening of Landau levels caused by considerable electron-electron scattering.
The low-temperature($4.2<T<12.5$ K) magnetotransport ($B<2$ T) of two-dimensional electrons occupying two subbands (with energy $E_1$ and $E_2$) is investigated in GaAs single quantum well with AlAs/GaAs superlattice barriers. Two series of Shubnikov-de Haas oscillations are found to be accompanied by magnetointersubband (MIS) oscillations, periodic in the inverse magnetic field. The period of the MIS oscillations obeys condition $Δ_{12}=(E_2-E_1)=k \cdot \hbar ω_c$, where $Δ_{12}$ is the subband energy separation, $ω_c$ is the cyclotron frequency, and $k$ is the positive integer. At $T$=4.2 K the oscillations manifest themselves up to $k$=100. Strong temperature suppression of the magnetointersubband oscillations is observed. We show that the suppression is a result of electron-electron scattering. Our results are in good agreement with recent experiments, indicating that the sensitivity to electron-electron interaction is the fundamental property of magnetoresistance oscillations, originating from the second-order Dingle factor.
The longitudinal resistivity of two dimensional (2D) electrons placed in strong magnetic field is significantly reduced by applied electric field, an effect which is studied in a broad range of magnetic fields and temperatures in GaAs quantum wells with high electron density. The data are found to be in good agreement with theory, considering the strong nonlinearity of the resistivity as result of non-uniform spectral diffusion of the 2D electrons. Inelastic processes limit the diffusion. Comparison with the theory yields the inelastic scattering time of the two dimensional electrons. In the temperature range T=2-10(K) for overlapping Landau levels, the inelastic scattering rate is found to be proportional to T^2, indicating a dominant contribution of the electron-electron scattering to the inelastic relaxation. In a strong magnetic field, the nonlinear resistivity demonstrates scaling behavior, indicating a specific regime of electron heating of well-separated Landau levels. In this regime the inelastic scattering rate is found to be proportional to T^3, suggesting the electron-phonon scattering as the dominant mechanism of the inelastic relaxation.
The non-linear zero-differential resistance state (ZDRS) that occurs for highly mobile two-dimensional electron systems in response to a dc bias in the presence of a strong magnetic field applied perpendicular to the electron plane is suppressed and disappears gradually as the magnetic field is tilted away from the perpendicular at fixed filling factor $ν$. Good agreement is found with a model that considers the effect of the Zeeman splitting of Landau levels enhanced by the in-plane component of the magnetic field.
Warming in complex physical systems, in particular global warming, attracts significant contemporary interest. It is essential, therefore, to understand basic physical mechanisms leading to overheating. It is well known that application of an electric field to conductors heats electric charge carriers. Often an elevated electron temperature describes the result of the heating. This paper demonstrates that an electric field applied to a conductor with discrete electron spectrum produces a non-equilibrium electron distribution, which cannot be described by temperature. Such electron distribution changes dramatically the conductivity of highly mobile two dimensional electrons in a magnetic field, forcing them into a state with a zero differential resistance. Most importantly the results demonstrate that, in general, the effective overheating in the systems with discrete spectrum is significantly stronger than the one in systems with continuous and homogeneous distribution of the energy levels at the same input power.
Zero differential resistance state is found in response to direct current applied to 2D electron systems at strong magnetic field and low temperatures. Transition to the state is accompanied by sharp dip of negative differential resistance, which occurs above threshold value $I_{th}$ of the direct current. The state depends significantly on the temperature and is not observable above several Kelvins. Additional analysis shows lack of the linear stability of the 2D electron systems at $I>I_{th}$ and inhomogeneous, non-stationary pattern of the electric current in the zero differential resistance state. We suggest that the dc bias induced redistribution of the 2D electrons in energy space is the dominant mechanism leading to the new electron state.
The effect of a microwave field in the frequency range from 54 to 140 $\mathrm{GHz}$ on the magnetotransport in a GaAs quantum well with AlAs/GaAs superlattice barriers and with an electron mobility no higher than $10^6$ $\mathrm{cm^2/Vs}$ is investigated. In the given two-dimensional system under the effect of microwave radiation, giant resistance oscillations are observed with their positions in magnetic field being determined by the ratio of the radiation frequency to the cyclotron frequency. Earlier, such oscillations had only been observed in GaAs/AlGaAs heterostructures with much higher mobilities. When the samples under study are irradiated with a 140-$\mathrm{GHz}$ microwave field, the resistance corresponding to the main oscillation minimum, which occurs near the cyclotron resonance, appears to be close to zero. The results of the study suggest that a mobility value lower than $10^6$ $\mathrm{cm^2/Vs}$ does not prevent the formation of zero-resistance states in magnetic field in a two-dimensional system under the effect of microwave radiation.
The effect of a DC electric field on the longitudinal resistance of highly mobile two dimensional electrons in heavily doped GaAs quantum wells is studied at different magnetic fields and temperatures. Strong suppression of the resistance by the electric field is observed in magnetic fields at which the Landau quantization of electron motion occurs. The phenomenon survives at high temperature where Shubnikov de Haas oscillations are absent. The scale of the electric fields essential for the effect is found to be proportional to temperature in the low temperature limit. We suggest that the strong reduction of the longitudinal resistance is the result of a nontrivial change in the distribution function of 2D electrons induced by the DC electric field. Comparison of the data with recent theory yields the inelastic electron-electon scattering time $τ_{in}$ and the quantum scattering time $τ_q$ of 2D electrons at high temperatures, a regime where previous methods were not successful.
The influence of microwave radiation (1.2-140 GHz) on resistance of high-mobility two-dimensional electron gas in GaAs quantum wells is studied. Two series of microwave-induced magnetoresistance oscillations periodic in 1/B were observed under microwave radiation. The periods of oscillations are determined by the microwave frequency and power, correspondingly. The experimental data is qualitatively explained by photon-assisted transport and Zener tunneling between Landau orbits.
We study the transport properties of a 2D electron gas in narrow GaAs quantum wells with AlAs/GaAs superlattice barriers. It is shown that the anisotropic positive magnetoresistance observed in selectively doped semiconductor structures in a parallel magnetic field is caused by the spatial modulation of the 2D electron gas.
We study the effect of random matter density fluctuations in the sun on resonant neutrino conversion in matter by solving numerically the evolution equation for the neutrino system including the full effect of the random matter density fluctuations of given amplitude and correlation length. In order to establish the possible effect on the MSW solutions to the solar neutrino problem we perform a global analysis of all the existing observables including the measured total rates as well as the Super-Kamiokande measurement on the time dependence of the event rates during the day and night and the recoil electron energy spectrum. We find the effects of random noise to be larger for small mixing angles and they are mostly important for correlation lengths in the range few 100 km $\lesssim L_0\lesssim$ few 1000 km. They can be understood as due to a parametric resonance occuring when the phase acquired by the oscillating neutrino state on one fluctuation length L_0 is a multiple of 2$π$. We find that this resonant parametric condition is mainly achieved for low energy neutrinos such as the pp-neutrinos and therefore its effect is mostly seen on the total event rates while the other Super-Kamiokande observables are very marginally sensitive to the presence of noise due to the higher energy threshold.
We have found allowed squared mass difference, magnetic field, mixing angle - regions for the Resonant Spin-Flavor Precession Solution to the Solar Neutrino Problem fitted with the data of all acting solar neutrino experiments. The typical mass difference region varying in dependence on the mixing angle is allowed for some discrete magnetic field regions in a wide range for the fixed neutrino transition magnetic moment. Except of the first allowed range with the lowest field strength the magnetic field amplitude within other discrete allowed regions depend essentially on the shape of a regular magnetic field profile in the convective zone of the Sun. For the non-zero neutrino mixing one can find at 99.9% C.L. an upper limit on the mixing, originated by the non-observation of electron antineutrinos in the SuperKamiokande detector. This limit occurs also sensitive to the magnetic field profile. While at 67% C.L. there is another more stringent upper limit coming from inconsistency of the gallium experiments with others. A new allowed region appears in the case of an additional assumption that the Homestake data are 1.3 times less than the experimental event rate.
The magnetic field in the solar convective zone has a random small-scale component with the r.m.s. value substancially exceeding the strength of a regular large-scale field. For two Majorana neutrino flavors and two helicities in the presence of a neutrino transition magnetic moment and nonzero neutrino mixing we analize the displacement of the allowed (Delta m^2 - sin^2 2theta)-parameter region reconciled for all Underground experiments with solar neutrinos in dependence on the r.m.s. magnetic field value b. In contrary with the RSFP scenario with a regular large-scale magnetic field, we find an effective production of electron antineutrinos in the Sun even for small neutrino mixing through the cascade conversions like nu_eL -> \bar{nu}_muR -> \bar{nu}_eR. It was found that usual SMA and LMA MSW parameter regions maybe forbidden while opening LOW MSW as the allowed one from the non-observation of \bar{nu}_eR in the SK experiment if random magnetic fields have strengths b > 100 kG and correlation lengths shorter than L_0 < 1000 km.
The magnetic field in the convective zone of the Sun has a random small-scale component with the r.m.s. value substantially exceeding the strength of a regular large-scale field. For two Majorana neutrino flavors $\times$ two helicities in the presence of a neutrino transition magnetic moment and nonzero neutrino mixing we analyze the displacement of the allowed ($Δm^2- \sin^22θ$)-parameter region reconciled for the SuperKamiokande(SK) and radiochemical (GALLEX, SAGE, Homestake) experiments in dependence on the r.m.s. magnetic field value $b$, or more precisely, on a value $μb$ assuming the transition magnetic moment $μ= 10^{-11}μ_B$. In contrast to RSFP in regular magnetic fields we find an effective production of electron antineutrinos in the Sun even for small neutrino mixing through cascade conversions $ν_{eL}\to ν_{μL}\to \tildeν_{eR}$, $ν_{eL}\to ν_{μR}\to \tildeν_{eR}$ in a random magnetic field that would be a signature of the Majorana nature of neutrino if $\tildeν_{eR}$ will be registered. Basing on the present SK bound on electron antineutrinos we have also found an excluded area in the same $Δm^2,~\sin^22θ$-plane and revealed a strong sensitivity to the random magnetic field correlation length $L_0$.
The magnetic field in the solar convective zone has a random small-scale component with the r.m.s. value substantially exceeding the strength of a regular large-scale field. For two Majorana neutrino flavors $\times$ two helicities in the presence of a neutrino transition magnetic moment and nonzero neutrino mixing we analyze the displacement of the allowed ($Δm^2 - \sin^22θ$) - parameter region reconciled for the SuperKamiokande(SK) and radiochemical (GALLEX, SAGE, Homestake) experiments in dependence on the r.m.s. magnetic field value $b$. We find an effective production of electron antineutrinos in the Sun even for small neutrino mixing through the cascade conversions in the random magnetic field that would be a signature of the Majorana nature of neutrino if $\tildeν_{eR}$ will be registered. Basing on the present SK bound on electron antineutrinos we also estimated the corresponding excluded area in the plane $Δm^2, \sin^22θ$.