42 research outputs found
Magnetoresistance Oscillations in Two-dimensional Electron Systems Induced by AC and DC Fields
We report on magnetotransport measurements in a high-mobility two-dimentional
electron system subject simultaneously to AC (microwave) and DC (Hall) fields.
We find that DC excitation affects microwave photoresistance in a nontrivial
way. Photoresistance maxima (minima) evolve into minima (maxima) and back,
reflecting strong coupling and interplay of AC- and DC-induced effects. Most of
our observations can be explained in terms of indirect electron transitions
using a new, ``combined'' resonant condition. Observed quenching of
microwave-induced zero resistance by a DC field cannot be unambiguously linked
to a domain model, at least until a systematic theory treating both excitation
types within a single framework is developed
Resonant Phonon Scattering in Quantum Hall Systems Driven by dc Electric Fields
Using dc excitation to spatially tilt Landau levels, we study resonant
acoustic phonon scattering in two-dimensional electron systems. We observe that
dc electric field strongly modifies phonon resonances, transforming resistance
maxima into minima and back into maxima. Further, phonon resonances are
enhanced dramatically in the non-linear dc response and can be detected even at
low temperatures. Most of our observations can be explained in terms of
dc-induced (de)tuning of the resonant acoustic phonon scattering and its
interplay with intra-Landau level impurity scattering. Finally, we observe a
dc-induced zero-differential resistance state and a resistance maximum which
occurs when the electron drift velocity approaches the speed of sound.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
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.Comment: 4 pages, 4 figure
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
, where 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.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Magnetotransport in a two-dimensional electron system in dc electric fields
We report on nonequilibrium transport measurements in a high-mobility
two-dimensional electron system subject to weak magnetic field and dc
excitation. Detailed study of dc-induced magneto-oscillations, first observed
by Yang {\em et al}., reveals a resonant condition that is qualitatively
different from that reported earlier. In addition, we observe dramatic
reduction of resistance induced by a weak dc field in the regime of separated
Landau levels. These results demonstrate similarity of transport phenomena in
dc-driven and microwave-driven systems and have important implications for
ongoing experimental search for predicted quenching of microwave-induced
zero-resistance states by a dc current.Comment: Revised version, to appear in Phys. Rev.
Non-linear magnetotransport in microwave-illuminated two-dimensional electron systems
We study magnetoresistivity oscillations in a high-mobility two-dimensional
electron system subject to both microwave and dc electric fields. First, we
observe that the oscillation amplitude is a periodic function of the inverse
magnetic field and is strongly suppressed at microwave frequencies near
half-integers of the cyclotron frequency. Second, we obtain a complete set of
conditions for the differential resistivity extrema and saddle points. These
findings indicate the importance of scattering without microwave absorption and
a special role played by microwave-induced scattering events antiparallel to
the electric field.Comment: 4 pages, 4 figure
Evidence for a New Dissipationless Regime in 2D Electronic Transport
In an ultra-clean 2D electron system (2DES) subjected to crossed
millimeterwave (30--150 GHz) and weak (B < 2 kG) magnetic fields, a series of
apparently dissipationless states emerges as the system is detuned from
cyclotron resonances. Such states are characterized by an exponentially
vanishing low-temperature longitudinal resistance and a classical Hall
resistance. The activation energies associated with such states exceeds the
Landau level spacing by an order of magnitude. Our findings are likely
indicative of a collective ground state previously unknown for 2DES.Comment: 4 pages, 2 figure
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.Comment: 4 pages, 3 figure
Observation of Apparently Zero-Conductance States in Corbino Samples
Using Corbino samples we have observed oscillatory conductance in a
high-mobility two-dimensional electron system subjected to crossed microwave
and magnetic fields. On the strongest of the oscillation minima the conductance
is found to be vanishingly small, possibly indicating an insulating state
associated with these minima.Comment: 4 pages, 3 figures, RevTex