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I. Yu. Smirnov

Publications and source records attributed to I. Yu. Smirnov.

At least 19 recordsLinked to original sources
arXiv2026

Magnetophonon Resistance Oscillations in Structures with a GaAs Quantum Well and Barriers of AlAs/GaAs$\langleδ$-Si$\rangle$ Superlattices

Magnetophonon resistance oscillations (MPR) associated with the resonant scattering of electrons by optical phonons at temperatures of 77-240 K, as well as resonant scattering of electrons by acoustic phonons (PIRO) at temperatures of 10-25 K, were investigated in the same samples featuring a GaAs quantum well and AlAs/GaAs superlattice barriers doped with Si. The study of MPR demonstrated that resonant electron scattering occurs on bulk longitudinal optical phonons and does not depend on the dimensionality of the system or inter-subband transitions in systems with two subbands of size quantization. However, the amplitude of the oscillation with number $N=1$ in two-dimensional structures depends on the interplay of scattering mechanisms, which, in turn, is influenced by the structure of the system. As for PIRO, in samples with two size quantization subbands, resonant electron scattering by longitudinal acoustic phonons is observed against the background of inter-subband transitions (MISO), leading to their interference.

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arXiv2026

AC Conductance in n-InSb Structures with Quantum Well. Acoustic Studies

We studied the ac conductance of an $n$-InSb quantum well structure using acoustic methods in magnetic fields up to 18 T and at temperatures ranging from 20 to 500 mK. We attribute the unusual magnetic field dependences of surface acoustic wave (SAW) attenuation and velocity observed in the experiment to the presence of a conducting layer parallel to the quantum well in the sample. We successfully separated the contributions from both the quantum well and the shunting layer, enabling the identification of their distinct conduction mechanisms. Furthermore, by employing the coincidence technique, we determined the electron g-factor in the quantum well and investigated its dependence on the degree of spin polarization.

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arXiv2023

Coexistence of two hole phases in high-quality $p$-GaAs/AlGaAs in the vicinity of Landau level filling factors $ν$=1 and $ν$=(1/3)

We focused on the transverse AC magneto-conductance of a high mobility $p$-GaAs/AlGaAs quantum well ($p=1.2\times 10^{11}$~cm$^{-2}$) in the vicinity of two values of the Landau level filling factor $ν$: $ν=1$ (integer quantum Hall effect) and $ν=1/3$ (fractional quantum Hall effect). The complex transverse AC conductance, $σ_{xx}^{AC} (ω)$, was found from simultaneous measurements of attenuation and velocity of surface acoustic waves (SAWs) propagating along the interface between a piezoelectric crystal and the two-dimensional hole system under investigation. We analyzed both the real and imaginary parts of the hole conductance and compared the similarities and differences between the results for filling factor 1 and filling factor 1/3. Both to the left and to the right of these values maxima of a specific shape, "wings", arose in the $σ(ν)$ dependences at those two $ν$. Analysis of the results of our acoustic measurements at different temperatures and surface acoustic wave frequencies allowed us to attribute these wings to the formation of collective localized states, namely the domains of a pinned Wigner crystal, i.e., a Wigner solid. While the Wigner solid has been observed in 2D hole systems previously, we were able to detect 20 it at the highest hole density and, therefore, the lowest hole-hole interaction reported.

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arXiv2021

Dresselhaus spin-orbit interaction in the p-AlGaAs/GaAs/AlGaAs structure with a square quantum well: Surface Acoustic Waves Study

The effect of spin-orbit interaction was studied in a high-quality $p$-AlGaAs/GaAs/AlGaAs structure with a square quantum well using acoustic methods. The structure grown on a GaAs (100) substrate was symmetrically doped with carbon on both sides of the quantum well. Shubnikov-de Haas-type oscillations of the ac conductance of two-dimensional holes were measured. At a low magnetic field $B <$2 T conductance oscillations undergo beating induced by a spin-orbit interaction. Analysis of the beating character made it possible to separate the conductance contributions from the two heavy holes subbands split by the spin-orbit interaction. For each of the subbands the values of the effective masses and quantum relaxation times have been determined, and then the energy of the spin-orbit interaction was obtained. The quantum well profile, as well as the small magnitude of the spin-orbit interaction, allowed us to conclude that the spin-orbit splitting is governed by the Dresselhaus mechanism.

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arXiv2020

Nonlinear AC and DC Conductivities in a Two-Subband n-GaAs/AlAs Heterostructure

The DC and AC conductivities of the n-GaAs/AlAs heterostructure with two filled size quantization levels are studied within a wide magnetic field range. The electron spectrum of such heterostructure is characterized by two subbands (symmetric $S$ and antisymmetric $AS$), separated by the band gap $Δ_{12}=15.5$ meV. It is shown that, in the linear regime at the applied magnetic field $B >3$ T, the system exhibits oscillations corresponding to the integer quantum Hall effect. A quite complicated pattern of such oscillations is well interpreted in terms of transitions between Landau levels related to different subbands. At $B <1$ T, magneto-intersubband resistance oscillations (MISOs) are observed. An increase in the conductivity with the electric current flowing across the sample or in the intensity of the surface acoustic wave (SAW) in the regime of the integer quantum Hall effect is determined by an increase in the electron gas temperature. In the case of intersubband transitions, it is found that nonlinearity cannot be explained by heating. At the same time, the decrease in the AC conductivity with increasing SAW electric field is independent of frequency, but the corresponding behavior does not coincide with that corresponding to the dependence of the DC conductivity on the Hall voltage $E_y$.

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arXiv2019

AC and DC Conductivities in an n-GaAs/AlAs Heterostructure with a Wide Quantum Well in the Integer Quantum Hall Effect Regime

The direct-current (dc) $σ_{xx}^{dc}$ and alternating-current (ac) $σ_{xx}^{ac}=σ_1-iσ_2$ conductivities of a wide (46 nm) GaAs quantum well with the bilayer electron density distribution are measured. It is found that the magnetic field dependence of $σ_{xx}$ exhibits three sets of oscillations related to the transitions between Landau levels in symmetric and antisymmetric subbands and with the transitions occurring owing to the Zeeman splitting of these subbands. The analysis of the frequency dependence of the ac conductivity and the $σ_1 / σ_2$ ratio demonstrates that the conductivity at the minima of oscillations is determined by the hopping mechanism.

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arXiv2019

Composite fermions in a wide quantum well in the vicinity of the filling factor 1/2

Using acoustic method we study dependences of transverse AC conductance, $σ(ω)$, on magnetic field, temperature and the amplitude of AC electric field in a wide (75 nm) quantum well (QW) structure focusing on the vicinity of the filling factor $ν=1/2$. Measurements are performed in the frequency domain 30-307 MHz and in the temperature domain 20-500 mK. Usually, in wide QW structures closely to $ν=1/2$ the fractional quantum Hall effect (FQHE) regime is realized at some parameters of the sample. However, in our structure, at $ν=1/2$ it is a compressible state corresponding to gas of composite fermions which is observed. This is confirmed by apparent frequency independence and weakly decreasing temperature dependence of $\mathrm{Re}\, σ(ω)$. Comparing the dependences of this quantity on temperature and power of the acoustic wave we conclude that the observed nonlinear behavior of the conductance is compatible with heating of the composite fermions by the acoustic wave. For comparison, we also study the vicinity of $ν= 3/2$ where the FQHE regime is clearly observed.

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arXiv2019

Electronic band structure in $n$-type GaAs/AlGaAs wide quantum wells in tilted magnetic field

Oscillations of the real component of AC conductivity $σ_1$ in a magnetic field were measured in the n-AlGaAs/GaAs structure with a wide (75 nm) quantum well by contactless acoustic methods at $T$=(20-500)~mK. In a wide quantum well, the electronic band structure is associated with the two-subband electron spectrum, namely the symmetric (S) and antisymmetric (AS) subbands formed due to electrostatic repulsion of electrons. A change of the oscillations amplitude in tilted magnetic field observed in the experiments occurs due to crossings of Landau levels of different subbands (S and AS) at the Fermi level. The theory developed in this work shows that these crossings are caused by the difference in the cyclotron energies in the S and AS subbands induced by the in-plane magnetic field.

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arXiv2018

Universal Frequency Dependence of the Hopping AC Conductance in p-Ge/GeSi Structures in the Integer Quantum Hall Effect Regime

The hopping ac conductance, which is realized at the transverse conductance minima in the regime of the integer Hall effect, has been measured using a combination of acoustic and microwave methods. Measurements have been made in the p-GeSi/Ge/GeSi structures with quantum wells in a wide frequency range (30-1200 MHz). The experimental frequency dependences of the real part of ac conductance $σ_1$ have been interpreted on the basis of the model presuming hops between localized electronic states belonging to isolated clusters. At high frequencies, dominating clusters are pairs of close states; upon a decrease in frequency, large clusters that merge into an infinite percolation cluster as the frequency tends to zero become important. In this case, the frequency dependences of the ac conductance can be represented by a universal curve. The scaling parameters and their magnetic-field dependence have been determined.

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arXiv2018

Effective g factor of 2D holes in strained Ge quantum wells

The effective g-factor of 2D holes in modulation doped \mbox{p-SiGe/Ge/SiGe} structures was studied. The AC conductivity of samples with hole densities from $3.9 \times 10^{11}$~to $6.2 \times 10^{11}~\text{cm}^{-2}$ was measured in perpendicular magnetic fields up to $8~\text{T}$ using a contactless acoustic method. From the analysis of the temperature dependence of conductivity oscillations, the $\mathrm{g}_{\perp}$-factor of each sample was determined. The $\mathrm{g}_{\perp}$-factor was found to be decreasing approximately linearly with hole density. This effect is attributed to non-parabolicity of the valence band.

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arXiv2018

Intersubband scattering in n-GaAs/AlGaAs wide quantum wells

Slow magnetooscilations of the conductivity are observed in a 75 nm wide quantum well at heating of the two-dimensional electrons by a high-intensity surface acoustic wave. These magnetooscillations are caused by intersubband elastic scattering between the symmetric and asymmetric subbands formed due to an electrostatic barrier in the center of the quantum well. The tunneling splitting between these subbands as well as the intersubband scattering rate are determined.

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arXiv2016

Melting of Wigner crystal in high-mobility $n$-GaAs/AlGaAs heterostructures at filling factors $0.18 > ν> 0.125$: Acoustic studies

Using acoustic methods the complex high-frequency conductance of high-mobility $n$-GaAs/AlGaAs heterostructures was determined in magnetic fields 12$÷$18~T. Based on the observed frequency and temperature dependences we conclude that in the investigated magnetic field range and at sufficiently low temperatures, $T \lesssim 200$~mK, the electron system forms a Wigner crystal deformed due to pinning by disorder. At some temperature, which depends on the electron filling factor, the temperature dependences of both components of the complex conductance get substantially changed. We have ascribed this rapid change of the conduction mechanism to melting of the Wigner crystal and study the dependence of the so-defined melting temperature on the electron filling factor.

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arXiv2015

Crossover between localized states and pinned Wigner crystal in high-mobility n-GaAs/AlGaAs heterostructures near filling factor $ν=1$

We have measured magnetic field dependences of the attenuation and velocity of surface acoustic waves in a high-mobility $n$-GaAs/AlGaAs structure with a wide quantum well. The results allowed us to find the complex conductance, $σ(ω)$, of the heterostructure for different frequencies, temperatures and magnetic fields near filling factors $ν=1, 2$. Observed behavior of $σ(ω)$ versus magnetic field outside close vicinities of integer fillings reveals an oscillation pattern indicative of the rich fractional quantum Hall effect. Our result is that in very close vicinities of integer filling factors the AC response of a high-mobility two-dimensional structures behaves as that of a two-dimensional system of localized electrons. Namely, both real and imaginary parts of the complex AC conductance at low temperatures agree with the predictions for the two-site model for a two-dimensional hopping system. Another result is the specific temperature dependences of $σ(ω)$, which are extremely sensitive to the filling factor value. These dependences indicate a sharp crossover between the localized modes and a pinned Wigner crystal.

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arXiv2015

Surface Acoustic Waves Probe of the Spin Phase Transition at $ν$=2/3 in n-GaAs/AlGaAs structure

High frequency (ac) conductivity in the single quantum well AlGaAs/GaAs/AlGaAs with high mobility was investigated by contactless acoustic methods in the fractional quantum Hall effect regime in perpendicular and tilted magnetic fields. We studied the dependence of ac conductivity $σ^{ac}=σ_1 - iσ_2$ on both the temperature and magnetic field tilt angle. Tilting the magnetic field relative to the sample surface enabled us to change the position of the conductivity oscillation minimum at $ν$=2/3. We measured the temperature dependence of ac conductivity for each tilt angle and for the 2/3 state we calculated the activation energy $ΔE$ which was derived by constructing the Arrhenius plot ln $σ_1$ against 1/$T$. Analyzing behavior of the activation energy in total magnetic field for the filling factor 2/3 we observed a distinct minimum which can be interpreted as the spin unpolarized-polarized phase transition.

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arXiv2015

Wigner crystal in a two-dimensional electron system in the vicinity of filling factor 1/5: Acoustic studies

By simultaneous measurements of the attenuation and velocity of surface acoustic waves propagating in proximity to a high-quality GaAs quantum well we study the complex AC conductance of the two-dimensional electron system. Focusing on the vicinity of the filling factor $ν=1/5$ we confirm that the insulating states formed closely to this value of $ν$ are pinned Wigner crystals.

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arXiv2014

In-plane magnetic field effect on hole cyclotron mass and $g_z$ factor in high-mobility SiGe/Ge/SiGe structures

The high-frequency (ac) conductivity of a high quality modulation doped GeSi/Ge/GeSi single quantum well structure with hole density $p$=6$\times$10$^{11}$cm$^{-2}$ was measured by the surface acoustic wave (SAW) technique at frequencies of 30 and 85~MHz and magnetic fields $B$ of up to 18 T in the temperature range of 0.3 -- 5.8 K. The acoustic effects were also measured as a function of the tilt angle of the magnetic field with respect to the normal of the two-dimensional channel at $T$=0.3 K. It is shown, that at the minima of the conductivity oscillations, holes are localized on the Fermi level, and that there is a temperature domain in which the high-frequency conductivity in the bulk of the quantum well is of the activation nature. The analysis of the temperature dependence of the conductivity at odd filling factors enables us to determine the effective $g_z$ factor. It is shown that the in-plane component of the magnetic field leads to an increase of the cyclotron mass and to a reduction of the $g_z$ factor. We developed a microscopic theory of these effects for the heavy-hole states of the complex valence band in quantum wells which describes well the experimental findings.

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arXiv2014

Contactless Measurement of AC Conductance in Quantum Hall Structures

We report a procedure to determine the frequency-dependent conductance of quantum Hall structures in a broad frequency domain. The procedure is based on the combination of two known probeless methods -- acoustic spectroscopy and microwave spectroscopy. By using the acoustic spectroscopy, we study the low-frequency attenuation and phase shift of a surface acoustic wave in a piezoelectric crystal in the vicinity of the electron (hole) layer. The electronic contribution is resolved using its dependence on a transverse magnetic field. At high frequencies, we study the attenuation of an electromagnetic wave in a coplanar waveguide. To quantitatively calibrate these data, we use the fact that in the quantum-Hall-effect regime the conductance at the maxima of its magnetic field dependence is determined by extended states. Therefore, it should be frequency independent in a broad frequency domain. The procedure is verified by studies of a well-characterized $p$-SiGe/Ge/SiGe heterostructure.

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