arXiv subjects

M. A. Zudov

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

At least 55 records · Page 3Linked to original sources

arXiv2013

Evidence for effective mass reduction in GaAs/AlGaAs quantum wells

We have performed microwave photoresistance measurements in high mobility GaAs/AlGaAs quantum wells and investigated the value of the effective mass. Surprisingly, the effective mass, obtained from the period of microwave-induced resistance oscillations, is found to be about 12% lower than the band mass in GaAs, $\mb$. This finding provides strong evidence for electron-electron interactions which can be probed by microwave photoresistance in very high Landau levels. In contrast, the measured magnetoplasmon dispersion revealed an effective mass which is close to $\mb$, in accord with previous studies.

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arXiv2013

Nonequilibrium phenomena in high Landau levels

Developments in the physics of 2D electron systems during the last decade have revealed a new class of nonequilibrium phenomena in the presence of a moderately strong magnetic field. The hallmark of these phenomena is magnetoresistance oscillations generated by the external forces that drive the electron system out of equilibrium. The rich set of dramatic phenomena of this kind, discovered in high mobility semiconductor nanostructures, includes, in particular, microwave radiation-induced resistance oscillations and zero-resistance states, as well as Hall field-induced resistance oscillations and associated zero-differential resistance states. We review the experimental manifestations of these phenomena and the unified theoretical framework for describing them in terms of a quantum kinetic equation. The survey contains also a thorough discussion of the magnetotransport properties of 2D electrons in the linear response regime, as well as an outlook on future directions, including related nonequilibrium phenomena in other 2D electron systems.

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arXiv2012

Microwave-induced resistance oscillations in tilted magnetic fields

We have studied the effect of an in-plane magnetic field on microwave-induced resistance oscillations in a high mobility two-dimensional electron system. We have found that the oscillation amplitude decays exponentially with an in-plane component of the magnetic field $B_\parallel$. While these findings cannot be accounted for by existing theories, our analysis suggests that the decay can be explained by a $B_\parallel$-induced correction to the quantum scattering rate, which is quadratic in $B_\parallel$.

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arXiv2012

Nonlinear response in overlapping and separated Landau levels of GaAs quantum wells

We have studied magnetotransport properties of a high-mobility two-dimensional electron system subject to weak electric fields. At low magnetic field $B$, the differential resistivity acquires a correction $δr \propto -λ^2 j^2/B^2$, where $λ$ is the Dingle factor and $j$ is the current density, in agreement with theoretical predictions. At higher magnetic fields, however, $δr$ becomes $B$-independent, $δr \propto -j^2$. While the observed change in behavior can be attributed to a crossover from overlapping to separated Landau levels, full understanding of this behavior remains a subject of future theories.

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arXiv2012

Shubnikov-de Haas oscillations in GaAs quantum wells in tilted magnetic fields

We report on quantum magneto-oscillations in an ultra-high mobility GaAs/AlGaAs quantum well at very high tilt angles. Unlike previous studies, we find that the spin and cyclotron splittings become equal over a continuous range of angles, but only near certain, angle-dependent filling factors. At high enough tilt angles, Shubnikov-de Haas oscillations reveal a prominent beating pattern, indicative of consecutive level crossings, all occurring at the same angle. We explain these unusual observations by an in-plane field-induced increase of the carrier mass, which leads to accelerated, filling factor-driven crossings of spin sublevels in tilted magnetic fields.

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arXiv2012

Magnetoplasmon resonance in 2D electron system driven into a zero-resistance state

We report on a remarkably strong, and a rather sharp, photoresistance peak originating from a dimensional magnetoplasmon resonance (MPR) in a high mobility GaAs/AlGaAs quantum well driven by microwave radiation into a zero-resistance state (ZRS). The analysis of the MPR signalreveals a negative background providing experimental evidence for the concept of absolute negative resistance associated with the ZRS. When a system is further subject to a dc field, the maxima of microwave-induced resistance oscillations decay away and a system reveals a state with close-to-zero differential resistance. The MPR peak, on the other hand, remains essentially unchanged, indicating surprisingly robust Ohmic behavior under the MPR conditions.

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arXiv2012

Giant negative magnetoresistance in high-mobility 2D electron systems

We report on a giant negative magnetoresistance in very high mobility GaAs/AlGaAs heterostructures and quantum wells. The effect is the strongest at $B \simeq 1$ kG, where the magnetoresistivity develops a minimum emerging at $T \lesssim 2$ K. Unlike the zero-field resistivity which saturates at $T \simeq 2 $ K, the resistivity at this minimum continues to drop at an accelerated rate to much lower temperatures and becomes several times smaller than the zero-field resistivity. Unexpectedly, we also find that the effect is destroyed not only by increasing temperature but also by modest in-plane magnetic fields. The analysis shows that giant negative magnetoresistance cannot be explained by existing theories considering interaction-induced or disorder-induced corrections.

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arXiv2011

Phase of phonon-induced resistance oscillations in a high-mobility two-dimensional electron gas

We report on experimental studies of magnetoresistance oscillations that originate from the resonant interaction of two-dimensional electrons with thermal transverse-acoustic phonons in very high-mobility GaAs/AlGaAs quantum wells. We find that the oscillation maxima consistently occur when a frequency of a phonon with twice the Fermi momentum exceeds an integer multiple of the cyclotron frequency. This observation is in contrast to to all previous experiments associating resistance maxima with magnetophonon resonance and its harmonics. Our experimentally obtained resonant condition is in excellent quantitative agreement with recent theoretical proposals.

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arXiv2011

Multiphoton microwave photoresistance in a high-mobility two-dimensional electron gas

We report on experimental and theoretical studies of microwave-induced resistance oscillations in a two-dimensional electron gas over a wide range of microwave intensities. We observe a distinct crossover from linear to sublinear power dependence of the oscillation amplitude and a concomitant narrowing of the oscillation extrema. To explain our observations we propose a theory based on the quantum kinetic equation at arbitrary microwave power. Taken together, these findings demonstrate a crucial role of multiphoton processes at elevated microwave intensities.

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arXiv2011

Microwave photoresistance in a two-dimensional electron gas with separated Landau levels

Theories of microwave-induced resistance oscillations in high-mobility two-dimensional electron gas predict that with decreasing oscillation order $n$ or with increasing frequency $ω$ the photoresistance maxima should appear closer to the cyclotron resonance harmonics due to increased Landau level separation. In this experimental study we demonstrate that while for a given $ω$ the peaks do move towards the harmonics with decreasing $n$, there is no corresponding movement with increasing $ω$ for a given $n$. These findings show that the positions of the photoresistance maxima cannot be directly linked to the Landau level separation challenging our current understanding of the phenomenon.

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arXiv2011

Giant microwave photoresistivity in a high-mobility quantum Hall system

We report the observation of a remarkably strong microwave photoresistivity effect in a high-mobility two-dimensional electron system subject to a weak magnetic field and low temperature. The effect manifests itself as a giant microwave-induced resistivity peak which, in contrast to microwave-induced resistance oscillations, appears only near the second harmonic of the cyclotron resonance and only at sufficiently high microwave frequencies. Appearing in the regime linear in microwave intensity, the peak can be more than an order of magnitude stronger than the microwave-induced resistance oscillations and cannot be explained by existing theories.

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arXiv2011

Non-linear response of a high mobility two-dimensional electron system near the second harmonic of the cyclotron resonance

Recent experiments on microwave-irradiated high-mobility two-dimensional electron systems revealed a novel photoresistivity peak in the vicinity of the second cyclotron resonance harmonic. Here we report on the nonlinear transport measurements and demonstrate that the peak can be induced by modest dc fields and that its position is not affected even by strong dc fields, in contrast to microwave-induced resistance oscillations that shift to higher magnetic fields. These findings reinforce the notion that the peak cannot be described by existing models and provides important constraints for further theoretical considerations.

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arXiv2011

Hall field-induced resistance oscillations in tilted magnetic fields

We have studied the effect of an in-plane magnetic field on Hall field-induced resistance oscillations in high mobility two-dimensional electron systems. We have found that the oscillation frequency depends only on the perpendicular component of the magnetic field but the oscillation amplitude decays exponentially with an in-plane component. While these findings cannot be accounted for by existing theories of nonlinear transport, our analysis suggests that the decay can be explained by an in-plane magnetic field-induced modification of the quantum scattering rate.

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arXiv2010

Zero differential resistance in two-dimensional electron systems at large filling factors

We report on a state characterized by a zero differential resistance observed in very high Landau levels of a high-mobility two-dimensional electron system. Emerging from a minimum of Hall field-induced resistance oscillations at low temperatures, this state exists over a continuous range of magnetic fields extending well below the onset of the Shubnikov-de Haas effect. The minimum current required to support this state is largely independent on the magnetic field, while the maximum current increases with the magnetic field tracing the onset of inter-Landau level scattering.

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arXiv2009

Non-linear Magnetoresistance Oscillations in Intensely Irradiated Two-Dimensional Electron Systems Induced by Multi-Photon Processes

We report on magneto-oscillations in differential resistivity of a two-dimensional electron system subject to intense microwave radiation. The period of these oscillations is determined not only by microwave frequency but also by its intensity. A theoretical model based on quantum kinetics at high microwave power captures all important characteristics of this phenomenon which is strongly nonlinear in microwave intensity. Our results demonstrate a crucial role of the multi-photon processes near the cyclotron resonance and its harmonics in the presence of strong dc electric field and offer a unique way to reliably determine the intensity of microwaves acting on electrons.

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arXiv2009

Role of electron-electron interactions in nonlinear transport in 2D electron systems

We study the temperature evolution of the non-linear oscillatory magnetoresistance in a high-mobility two-dimensional electron system subject to a strong dc electric field. We find that the decay of the oscillation amplitude with increasing temperature originates primarily from increasing quantum scattering rate entering the Dingle factor. We attribute this behavior to electron-electron interaction effects.

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arXiv2009

Phonon-induced Resistance Oscillations in Very-high Mobility 2D Electron Systems

We report on temperature dependence of acoustic phonon-induced resistance oscillations in very high mobility two-dimensional electron systems. We observe that the temperature dependence is non-monotonic and that higher order oscillations are best developed at progressively lower temperatures. Our analysis shows that, in contrast to Shubnikov-de Haas effect, phonon-induced resistance oscillations are sensitive to electron-electron interactions modifying the single particle lifetime.

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arXiv2009

Temperature Dependence of Microwave Photoresistance in 2D Electron Systems

We report on the temperature dependence of microwave-induced resistance oscillations in high-mobility two-dimensional electron systems. We find that the oscillation amplitude decays exponentially with increasing temperature, as $\exp(-αT^2)$, where $α$ scales with the inverse magnetic field. This observation indicates that the temperature dependence originates primarily from the modification of the single particle lifetime, which we attribute to electron-electron interaction effects.

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