arXiv subjects

O. E. Raichev

Publications and source records attributed to O. E. Raichev.

At least 37 records · Page 2Linked to original sources

arXiv2013

Transition from insulating to metallic phase induced by in-plane magnetic field in HgTe quantum wells

We report transport measurements in HgTe-based quantum wells with well width of 8 nm, corresponding to quantum spin Hall state, subject to in-plane magnetic field. In the absence of the magnetic field the local and nonlocal resistances behave very similar, which confirms the edge state transport in our system. In the magnetic field, we observe a monotonic decrease of the resistance with saturation of local resistance, while nonlocal resistance disappears completely, independent of the gate voltage. We believe that these evidences of metallic behavior indicate a transition to a gapless two-dimensional phase, according to theoretical predictions. The influence of disorder on resistivity properties of HgTe quantum wells under in-plane magnetic field is discussed.

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arXiv2012

Unconventional Hall effect near charge neutrality point in a two-dimensional electron-hole system

The transport properties of the two-dimensional system in HgTe-based quantum wells containing simultaneously electrons and holes of low densities are examined. The Hall resistance, as a function of perpendicular magnetic field, reveals an unconventional behavior, different from the classical N-shaped dependence typical for bipolar systems with electron-hole asymmetry. The quantum features of magnetotransport are explained by means of numerical calculation of the Landau level spectrum based on the Kane Hamiltonian. The origin of the quantum Hall plateau σxy = 0 near the charge neutrality point is attributed to special features of Landau quantization in our system.

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arXiv2011

Non-linear transport phenomena in a two-subband system

We study non-linear transport phenomena in a high-mobility bilayer system with two closely spaced populated electronic subbands in a perpendicular magnetic field. For a moderate direct current excitation, we observe zero-differential-resistance states with a characteristic 1/B periodicity. We investigate, both experimentally and theoretically, the Hall field-induced resistance oscillations which modulate the high-frequency magneto-intersubband oscillations in our system if we increase the current. We also observe and describe the influence of direct current on the magnetoresistance in the presence of microwave irradiation.

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arXiv2011

Microwave-induced Hall resistance in bilayer electron systems

The influence of microwave irradiation on dissipative and Hall resistance in high-quality bilayer electron systems is investigated experimentally. We observe a deviation from odd symmetry under magnetic field reversal in the microwave-induced Hall resistance $ΔR_{xy}$ whereas the dissipative resistance $ΔR_{xx}$ obeys even symmetry. Studies of $ΔR_{xy}$ as a function of the microwave electric field and polarization exhibit a strong and non-trivial power and polarization dependence. The obtained results are discussed in connection to existing theoretical models of microwave-induced photoconductivity.

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arXiv2011

Evidence for zero-differential resistance states in electronic bilayers

We observe zero-differential resistance states at low temperatures and moderate direct currents in a bilayer electron system formed by a wide quantum well. Several regions of vanishing resistance evolve from the inverted peaks of magneto-intersubband oscillations as the current increases. The experiment, supported by a theoretical analysis, suggests that the origin of this phenomenon is based on instability of homogeneous current flow under conditions of negative differential resistivity which leads to formation of current domains in our sample, similar to the case of single-layer systems.

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arXiv2010

Thermally activated intersubband scattering and oscillating magnetoresistance in quantum wells

Experimental studies of magnetoresistance in high-mobility wide quantum wells reveal oscillations which appear with an increase in temperature to 10 K and whose period is close to that of Shubnikov-de Haas oscillations. The observed phenomenon is identified as magnetointersubband oscillations caused by the scattering of electrons between two occupied subbands and the third subband which becomes occupied as a result of thermal activation. These small-period oscillations are less sensitive to thermal suppression than the largeperiod magnetointersubband oscillations caused by the scattering between the first and the second subbands. Theoretical study, based on consideration of electron scattering near the edge of the third subband, gives a reasonable explanation of our experimental findings.

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arXiv2010

Microwave zero-resistance states in a bilayer electron system

Magnetotransport measurements on a high-mobility electron bilayer system formed in a wide GaAs quantum well reveal vanishing dissipative resistance under continuous microwave irradiation. Profound zero-resistance states (ZRS) appear even in the presence of additional intersubband scattering of electrons. We study the dependence of photoresistance on frequency, microwave power. and temperature. Experimental results are compared with a theory demonstrating that the conditions for absolute negative resistivity correlate with the appearance of ZRS.

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arXiv2010

Theory of acoustic-phonon assisted magnetotransport in 2D electron systems at large filling factors

A microscopic theory of the phonon-induced resistance oscillations in weak perpendicular magnetic fields is presented. The calculations are based on the consideration of interaction of two-dimensional electrons with three-dimensional (bulk) acoustic phonons and take into account anisotropy of the phonon spectrum in cubic crystals. The magnetoresistance is calculated for [001]-grown GaAs quantum wells. The results are in agreement with available experimental data. Apart from the numerical results, analytical expressions for the oscillating part of magnetoresistance are obtained. These expressions are valid in the region of high-order magnetophonon resonances and describe the oscillating magnetoresistance determined by several groups of phonons polarized along certain high-symmetry directions.

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arXiv2010

Microwave-induced magnetoresistance of two-dimensional electrons interacting with acoustic phonons

The influence of electron-phonon interaction on magnetotransport in two-dimensional electron systems under microwave irradiation is studied theoretically. Apart from the phonon-induced resistance oscillations which exist in the absence of microwaves, the magnetoresistance of irradiated samples contains oscillating contributions due to electron scattering on both impurities and acoustic phonons. The contributions due to electron-phonon scattering are described as a result of the interference of phonon-induced and microwave-induced resistance oscillations. In addition, microwave heating of electrons leads to a special kind of phonon-induced oscillations. The relative strength of different contributions and their dependence on parameters are discussed. The interplay of numerous oscillating contributions suggests a peculiar magnetoresistance picture in high-mobility layers at the temperatures when electron-phonon scattering becomes important.

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arXiv2010

Crossover between distinct mechanisms of microwave photoresistance in bilayer systems

We report on temperature-dependent magnetoresistance measurements in balanced double quantum wells exposed to microwave irradiation for various frequencies. We have found that the resistance oscillations are described by the microwave-induced modification of electron distribution function limited by inelastic scattering (inelastic mechanism), up to a temperature of T*~4 K. With increasing temperature, a strong deviation of the oscillation amplitudes from the behavior predicted by this mechanism is observed, presumably indicating a crossover to another mechanism of microwave photoresistance, with similar frequency dependence. Our analysis shows that this deviation cannot be fully understood in terms of contribution from the mechanisms discussed in theory.

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arXiv2009

Magnetoresistance oscillations in multilayer systems - triple quantum wells

Magnetoresistance of two-dimensional electron systems with several occupied subbands oscillates owing to periodic modulation of the probability of intersubband transitions by the quantizing magnetic field. In addition to previous investigations of these magneto-intersubband (MIS) oscillations in two-subband systems, we report on both experimental and theoretical studies of such a phenomenon in three-subband systems realized in triple quantum wells. We show that the presence of more than two subbands leads to a qualitatively different MIS oscillation picture, described as a superposition of several oscillating contributions. Under a continuous microwave irradiation, the magnetoresistance of triple-well systems exhibits an interference of MIS oscillations and microwaveinduced resistance oscillations. The theory explaining these phenomena is presented in the general form, valid for an arbitrary number of subbands. A comparison of theory and experiment allows us to extract temperature dependence of quantum lifetime of electrons and to confirm the applicability of the inelastic mechanism of microwave photoresistance for the description of magnetotransport in multilayer systems.

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arXiv2009

High order fractional microwave induced resistance oscillations in 2D systems

We report on the observation of microwave-induced resistance oscillations associated with the fractional ratio n/m of the microwave irradiation frequency to the cyclotron frequency for m up to 8 in a two-dimensional electron system with high electron density. The features are quenched at high microwave frequencies independent of the fractional order m. We analyze temperature, power, and frequency dependencies of the magnetoresistance oscillations and discuss them in connection with existing theories.

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arXiv2008

Nonlinear transport and oscillating magnetoresistance in double quantum wells

We study the evolution of low-temperature magnetoresistance in double quantum wells in the region below 1 Tesla as the applied current density increases. A flip of the magneto-intersubband oscillation peaks, which occurs as a result of the current-induced inversion of the quantum component of resistivity, is observed. We also see splitting of these peaks as another manifestation of nonlinear behavior, specific for the two-subband electron systems. The experimental results are quantitatively explained by the theory based on the kinetic equation for the isotropic non-equilibrium part of electron distribution function. The inelastic scattering time is determined from the dependence of the inversion magnetic field on the current.

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arXiv2008

Interference oscillations of microwave photoresistance in double quantum wells

We observe oscillatory magnetoresistance in double quantum wells under microwave irradiation. The results are explained in terms of the influence of subband coupling on the frequency-dependent photoinduced part of the electron distribution function. As a consequence, the magnetoresistance demonstrates the interference of magneto-intersubband oscillations and conventional microwave- induced resistance oscillations.

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arXiv2008

Resonance oscillations of magnetoresistance in double quantum wells

We present experimental and theoretical studies of the magnetoresistance oscillations induced by resonance transitions of electrons between tunnel-coupled states in double quantum wells. The suppression of these oscillations with increasing temperature is irrelevant to the thermal broadening of the Fermi distribution and reflects the temperature dependence of the quantum lifetime of electrons. The gate control of the period and amplitude of the oscillations is demonstrated.

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arXiv2007

Frequency dependence of induced spin polarization and spin current in quantum wells

Dynamic response of two-dimensional electron systems with spin-orbit interaction is studied theoretically on the basis of quantum kinetic equation, taking into account elastic scattering of electrons. The spin polarization and spin current induced by the applied electric field are calculated for the whole class of electron systems described by p-linear spin-orbit Hamiltonians. The absence of nonequilibrium intrinsic static spin currents is confirmed for these systems with arbitrary (nonparabolic) electron energy spectrum. Relations between the spin polarization, spin current, and electric current are established. The general results are applied to the quantum wells grown in [001] and [110] crystallographic directions, with both Rashba and Dresselhaus types of spin-orbit coupling. It is shown that the existence of the fixed (momentum-independent) precession axes in [001]-grown wells with equal Rashba and Dresselhaus spin velocities or in symmetric [110]-grown wells leads to vanishing spin polarizability at arbitrary frequency of the applied electric field. This property is explained by the absence of Dyakonov-Perel-Kachorovskii spin relaxation for the spins polarized along these precession axes. As a result, a considerable frequency dispersion of spin polarization at very low frequency in the vicinity of the fixed precession axes is predicted. Possible effects of extrinsic spin-orbit coupling on the obtained results are discussed.

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arXiv2007

Spin magnetotransport in two-dimensional hole systems

Spin current of two-dimensional holes occupying the ground-state subband in an asymmetric quantum well and interacting with static disorder potential is calculated in the presence of a weak magnetic field H perpendicular to the well plane. Both spin-orbit coupling and Zeeman coupling are taken into account. It is shown that the applied electric field excites both the transverse (spin-Hall) and diagonal spin currents, the latter changes its sign at a finite H and becomes greater than the spin-Hall current as H increases. The effective spin-Hall conductivity introduced to describe the spin response in Hall bars is considerably enhanced by the magnetic field in the case of weak disorder and demonstrates a non-monotonic dependence on H.

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arXiv2007

Intrinsic Spin Hall Effect: Topological Transitions in Two-Dimensional Systems

The spin-Hall conductivity in spatially-homogeneous two-dimensional electron systems described by the spin-orbit Hamiltonian \hbar Ω_p σis presented as a sum of the universal part Me/8 π\hbar determined by the Berry phase Φ=M π(M is an odd integer, the winding number of the vector Ω_p) and a non-universal part which vanishes under certain conditions determined by the analytical properties of Ω_p. The analysis reveals a rich and complicated behavior of the spin-Hall conductivity which is relevant to both electron and hole states in quantum wells and can be detected in experiments.

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