arXiv subjects

M. A. Zudov

Publications and source records attributed to M. A. Zudov.

At least 19 recordsLinked to original sources

arXiv2026

Radiowave-induced Resistance Oscillations

Microwave-induced resistance oscillations (MIROs) occur when a 2D electron gas is subjected to radiation of frequency $ω= 2 πf$ and varying magnetic field $B$. MIROs are periodic in $1/B$, with the period determined by the radiation frequency $ω$, and their amplitude scales with the radiation power. Stepping from single-photon transitions between Landau levels, MIROs are found on the low-field side of the cyclotron resonance, $ω_c \lesssim ω$, where $ω_c$ is the cyclotron frequency. Here, we report on another class of magneto resistance oscillations, which are induced by high-intensity radiation in the radio frequency range and occur at $ω_c \gg ω$. These oscillations are independent of frequency $ω$, can be either $1/B$ or $1/B^2$-periodic, and their period is controlled by the radiation electric field. We further show that using a displacement model in the limit of short-range (``sharp'') disorder we can extract the radiation field and the width of the cyclotron resonance.

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arXiv2026

Oscillatory photoresistance on the high field side of the cyclotron resonance

We consider the displacement contribution to photoresistance in overlapping Landau levels at radiation frequencies much smaller than the cyclotron frequency. We show that in the limit of short-range disorder and high radiation power, this contribution leads to a new class of magneto-resistance oscillations. These oscillations, which we call radiowave-induced resistance oscillations (RIROs), are distinct from the well known microwave-induced resistance oscillations in the following aspects: (i) their amplitude is independent of power, (ii) their period is controlled by the radiation electric field, rather than by the radiation frequency, and (iii) they can be either $1/B$ or $1/B^2$-periodic, depending on $B$, with the crossover point linked to the width of the cyclotron resonance absorption curve. We also show that RIROs should be readily observed in experiments.

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arXiv2025

High-order two-component fractional quantum Hall states around filling factor $ν= 1$

Two-component fractional quantum Hall (2C-FQH) states in electron bilayers have been known for decades, yet their experimental realization remained limited to low-order fractions. Here we report on several families of high-order 2C-FQH states that emerge when an in-plane magnetic field drives a controlled monolayer-to-bilayer transition in an ultra-high-mobility GaAs quantum well. These families of states proliferate symmetrically toward the filling factor $ν= 1$, from both $ν= 2/3$ and $ν= 4/3$, thereby respecting particle-hole symmetry. Surprisingly, many unbalanced states (with unequal layer fillings) are more robust than their parent balanced states, defying the expected hierarchy of Jain sequences. Our findings substantially expand the known landscape of 2C-FQH states, highlighting the unexpected richness of the bilayer quantum Hall regime and opening new routes for probing the interplay of symmetry, topology, and interactions in quantum Hall systems.

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arXiv2025

How to accurately measure the mobility and viscosity of two-dimensional carriers?

Two different methods of \emph{metrological} accuracy are proposed to determine the mobility and viscosity of ultra clean two-dimensional electron liquids. The experimental data analysis is based on the Gurzhi hydrodynamic model under no-slip boundary conditions without preliminary assumptions about carrier scattering times. The applicability of no-slip boundary conditions has been proven. A Hall bar with several conducting channels of different widths in a zero magnetic field and a sample with a single channel in a perpendicular field are considered. In both cases, it was possible to accurately isolate the ohmic part of the total measured resistance and, then find the exact mobility and viscosity of the charge liquid. The extracted e-e scattering time is extremely close to that obtained by other experimental group for transport measurements of superballistic point contact. At low temperatures the e-e scattering time demonstrates a stronger dependence compare to $1/T^{2}$ behavior predicted by Fermi liquid theory. We propose both methods as powerful tools for viscometry and finding the mobility of two-dimensional systems.

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arXiv2022

Scattering mechanisms in state-of-the-art GaAs/AlGaAs quantum wells

Motivated by recent breakthrough in molecular beam epitaxy of GaAs/AlGaAs quantum wells [Y. J. Chung \textit{et al.}, Nature Materials \textbf{20}, 632 (2021)], we examine contributions to mobility and quantum mobility from various scattering mechanisms and their dependencies on the electron density. We find that at lower electron densities, $n_e \lesssim 1 \times 10^{11}$ cm$^{-2}$, both transport and quantum mobility are limited by unintentional background impurities and follow a power law dependence, $\propto n_e^α$, with $α\approx 0.85$. Our predictions for quantum mobility are in reasonable agreement with an estimate obtained from the resistivity at filling factor $ν= 1/2$ in a sample of Y. J. Chung \textit{et al.} with $n_e = 1 \times 10^{11}$ cm$^{-2}$. Consideration of other scattering mechanisms indicates that interface roughness (remote donors) is a likely limiting factor of transport (quantum) mobility at higher electron densities. Future measurements of quantum mobility should yield information on the distribution of background impurities in GaAs and AlGaAs.

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arXiv2021

Anomalous nematic-to-stripe phase transition driven by in-plane magnetic fields

Anomalous nematic states, recently discovered in ultraclean two-dimensional electron gas, emerge from quantum Hall stripe phases upon further cooling. These states are hallmarked by a local minimum (maximum) in the hard (easy) longitudinal resistance and by an incipient plateau in the Hall resistance in nearly half-filled Landau levels. Here, we demonstrate that a modest in-plane magnetic field, applied either along $\left < 110 \right >$ or $\left < 1\bar10 \right >$ crystal axis of GaAs, destroys anomalous nematic states and restores quantum Hall stripe phases aligned along their native $\left < 110 \right >$ direction. These findings confirm that anomalous nematic states are distinct from other ground states and will assist future theories to identify their origin.

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arXiv2020

Hidden Quantum Hall Stripes in Al$_{x}$Ga$_{1-x}$As/Al$_{0.24}$Ga$_{0.76}$As Quantum Wells

We report on transport signatures of hidden quantum Hall stripe (hQHS) phases in high ($N > 2$) half-filled Landau levels of Al$_{x}$Ga$_{1-x}$As/Al$_{0.24}$Ga$_{0.76}$As quantum wells with varying Al mole fraction $x < 10^{-3}$. Residing between the conventional stripe phases (lower $N$) and the isotropic liquid phases (higher $N$), where resistivity decreases as $1/N$, these hQHS phases exhibit isotropic and $N$-independent resistivity. Using the experimental phase diagram we establish that the stripe phases are more robust than theoretically predicted, calling for improved theoretical treatment. We also show that, unlike conventional stripe phases, the hQHS phases do not occur in ultrahigh mobility GaAs quantum wells, but are likely to be found in other systems.

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arXiv2020

Isotropically conducting (hidden) quantum Hall stripe phases in a two-dimensional electron gas

Quantum Hall stripe (QHS) phases, predicted by the Hartree-Fock theory, are manifested in GaAs-based two-dimensional electron gases as giant resistance anisotropies. Here, we predict a ``hidden'' QHS phase which exhibits \emph{isotropic} resistivity whose value, determined by the density of states of QHS, is independent of the Landau index $N$ and is inversely proportional to the Drude conductivity at zero magnetic field. At high enough $N$, this phase yields to an Ando-Unemura-Coleridge-Zawadski-Sachrajda phase in which the resistivity is proportional to $1/N$ and to the ratio of quantum and transport lifetimes. Experimental observation of this border should allow one to find the quantum relaxation time.

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arXiv2020

Anomalous Nematic States in High Half-Filled Landau Levels

It is well established that the ground states of a two-dimensional electron gas with half-filled high ($N \ge 2$) Landau levels are compressible charge-ordered states, known as quantum Hall stripe (QHS) phases. The generic features of QHSs are a maximum (minimum) in a longitudinal resistance $R_{xx}$ ($R_{yy}$) and a non-quantized Hall resistance $R_H$. Here, we report on emergent minima (maxima) in $R_{xx}$ ($R_{yy}$) and plateau-like features in $R_H$ in half-filled $N \ge 3$ Landau levels. Remarkably, these unexpected features develop at temperatures considerably lower than the onset temperature of QHSs, suggesting a new ground state.

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arXiv2020

Effect of Berry Phase on Nonlinear Response of Two-dimensional Fermions

We develop a theory of nonlinear response to an electric field of two-dimensional (2D) fermions with topologically non-trivial wave functions characterized by the Berry phase $Φ_n = n π, n = 1,2,...$. In particular, we find that owing to suppression of backscattering at odd $n$, Hall field-induced resistance oscillations, which stem from elastic electron transitions between Hall field-tilted Landau levels, are qualitatively distinct from those at even $n$: their amplitude decays with the electric field and their extrema are phase-shifted by a quarter cycle. The theory unifies the cases of graphene ($n = 1$) and graphite bilayer ($n = 2$) with the case of conventional 2D electron gas ($n = 0$) and suggests a new method to probe backscattering in topological 2D systems.

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arXiv2019

Effect of density on microwave-induced resistance oscillations in back-gated GaAs quantum wells

We report on microwave-induced resistance oscillations (MIROs) in a tunable-density 30-nm-wide GaAs/AlGaAs quantum well. We find that the MIRO amplitude increases dramatically with carrier density. Our analysis shows that the anticipated increase in the effective microwave power and quantum lifetime with density is not sufficient to explain the observed growth of the amplitude. We further observe that the fundamental oscillation extrema move towards cyclotron resonance with increasing density, which also contradicts theoretical predictions. These findings reveal that the density dependence is not properly captured by existing theories, calling for further studies.

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arXiv2019

Effect of illumination on quantum lifetime in GaAs quantum wells

Low-temperature illumination of a two-dimensional electron gas in GaAs quantum wells is known to greatly improve the quality of high-field magnetotransport. The improvement is known to occur even when the carrier density and mobility remain unchanged, but what exactly causes it remains unclear. Here, we investigate the effect of illumination on microwave photoresistance in low magnetic fields. We find that the amplitude of microwave-induced resistance oscillations grows dramatically after illumination. Dingle analysis reveals that this growth reflects a substantial increase in the single-particle (quantum) lifetime, which likely originates from the light-induced redistribution of charge enhancing the screening capability of the doping layers.

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arXiv2019

Quantum Hall stripes in high-density GaAs/AlGaAs quantum wells

We report on quantum Hall stripes (QHSs) formed in higher Landau levels of GaAs/AlGaAs quantum wells with high carrier density ($n_e > 4 \times 10^{11}$ cm$^{-2}$) which is expected to favor QHS orientation along unconventional $\left < 1\bar{1}0 \right >$ crystal axis and along the in-plane magnetic field $B_{||}$. Surprisingly, we find that at $B_{||} = 0$ QHSs in our samples are aligned along $\left < 110 \right >$ direction and can be reoriented only perpendicular to $B_{||}$. These findings suggest that high density alone is not a decisive factor for either abnormal native QHS orientation or alignment with respect to $B_{||}$, while quantum confinement of the 2DEG likely plays an important role.

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arXiv2019

Two- and three-electron bubbles in Al$_{x}$Ga$_{1-x}$As/Al$_{0.24}$Ga$_{0.76}$As quantum wells

We report on transport signatures of eight distinct bubble phases in the $N=3$ Landau level of a Al$_{x}$Ga$_{1-x}$As/Al$_{0.24}$Ga$_{0.76}$As quantum well with $x = 0.0015$. These phases occur near partial filling factors $ν^\star \approx 0.2\,(0.8)$ and $ν^\star \approx 0.3\,(0.7)$ and have $M = 2$ and $M = 3$ electrons (holes) per bubble, respectively. We speculate that a small amount of alloy disorder in our sample helps to distinguish these broken symmetry states in low-temperature transport measurements.

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arXiv2018

Mobility and quantum mobility of modern GaAs/AlGaAs heterostructures

In modern GaAs/Al$_x$Ga$_{1-x}$As heterostructures with record high mobilities, a two-dimensional electron gas (2DEG) in a quantum well is provided by two remote donor $δ$-layers placed on both sides of the well. Each $δ$-layer is located within a narrow GaAs well, flanked by narrow AlAs layers which capture excess electrons from donors. We show that each excess electron is localized in a compact dipole atom with the nearest donor. Nevertheless, excess electrons screen both the remote donors and background impurities. When the fraction of remote donors filled by excess electrons $f$ is small, the remote donor limited quantum mobility grows as $f^{3}$ and becomes larger than the background impurity limited one at a characteristic value $f_c$. We also calculate both the mobility and the quantum mobility limited by the screened background impurities with concentrations $N_1$ in Al$_x$Ga$_{1-x}$As and $N_2$ in GaAs, which allows one to estimate $N_1$ and $N_2$ from the measured mobilities. Taken together, our findings should help to identify avenues for further improvement of modern heterostructures.

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arXiv2017

Microwave-induced resistance oscillations in a back-gated GaAs quantum well

We performed effective mass measurements employing microwave-induced resistance oscillation in a tunable-density GaAs/AlGaAs quantum well. Our main result is a clear observation of an effective mass increase with decreasing density, in general agreement with earlier studies which investigated the density dependence of the effective mass employing Shubnikov- de Haas oscillations. This finding provides further evidence that microwave-induced resistance oscillations are sensitive to electron-electron interactions and offer a convenient and accurate way to obtain the effective mass.

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arXiv2017

Bloch-Grüneisen nonlinearity of electron transport in GaAs/AlGaAs heterostructures

We report on nonlinear transport measurements in a two-dimensional electron gas hosted in GaAs/AlGaAs heterostructures. Upon application of direct current, the low-temperature differential resistivity acquires a positive correction, which exhibits a pronounced maximum followed by a plateau. With increasing temperature, the nonlinearity diminishes and disappears. These observations can be understood in terms of a crossover from the Bloch-Grüneisen regime to the quasielastic scattering regime as the electrons are heated by direct current. Calculations considering the interaction of electrons with acoustic phonons provide a reasonable description of our experimental findings.

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arXiv2017

Hall field-induced resistance oscillations in a tunable-density GaAs quantum well

We report on Hall field-induced resistance oscillations (HIRO) in a 60 nm-wide GaAs/AlGaAs quantum well with an \emph{in situ} grown back gate, which allows tuning the carrier density $n$. At low $n$, when all electrons are confined to the lowest subband (SB1), the HIRO frequency, proportional to the product of the cyclotron diameter and the Hall field, scales with $n^{-1/2}$, as expected. Remarkably, population of the second subband (SB2) significantly enhances HIRO, while their frequency now scales as $n^{-1}$. We demonstrate that in this two-subband regime HIRO still originate solely from backscattering of SB1 electrons. The unusual density dependence occurs because the population of SB2 steadily increases, while that of SB1 remains essentially unchanged. The enhancement of HIRO manifests an unexpected, step-like increase of the quantum lifetime of SB1 electrons, which reaches a record value of 52 ps in the two-subband regime.

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