192 research outputs found

### Coulombic effects on magnetoconductivity oscillations induced by microwave excitation in multisubband two-dimensional electron systems

We develop a theory of magneto-oscillations in photoconductivity of
multisubband two-dimensional electron systems which takes into account strong
Coulomb interaction between electrons. In the presence of a magnetic field
oriented perpendicular, internal electric fields of fluctuational origin cause
fast drift velocities of electron orbit centers which affect probabilities of
inter-subband scattering and the photoconductivity. For the electron system
formed on the liquid helium surface, internal forces are shown to suppress the
amplitude of magneto-oscillations, and change positions of magnetoconductivity
minima which evolve in zero-resistance states for high radiation power.Comment: 9 pages, 6 figure

### 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.Comment: 12 pages, 2 figure

### Microwave-resonance-induced magnetooscillations and vanishing resistance states in multisubband two-dimensional electron systems

The dc magnetoconductivity of the multisubband two-dimensional electron
system formed on the liquid helium surface in the presence of resonant
microwave irradiation is described, and a new mechanism of the negative linear
response conductivity is studied using the self-consistent Born approximation.
Two kinds of scatterers (vapor atoms and capillary wave quanta) are considered.
Besides a conductivity modulation expected near the points, where the
excitation frequency for inter-subband transitions is commensurate with the
cyclotron frequency, a sign-changing correction to the linear conductivity is
shown to appear for usual quasi-elastic inter-subband scattering, if the
collision broadening of Landau levels is much smaller than thermal energy. The
decay heating of the electron system near the commensurability points leads to
magnetooscillations of electron temperature, which are shown to increase the
importance of the sign-changing correction. The line shape of
magnetoconductivity oscillations calculated for wide ranges of temperature and
magnetic field is in a good accordance with experimental observations.Comment: 13 pages, 8 figure

### 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.Comment: 8 pages, 6 figure

### The fine structure of microwave-induced magneto-oscillations in photoconductivity of the two-dimensional electron system formed on a liquid-helium surface

The influence of the inelastic nature of electron scattering by surface
excitations of liquid helium (ripplons) on the shape of magnetoconductivity
oscillations induced by resonance microwave (MW) excitation is theoretically
studied. The MW field provides a substantial filling of the first excited
surface subband which sparks off inter-subband electron scattering by ripplons.
This scattering is the origin of magneto-oscillations in the momentum
relaxation rate. The inelastic effect becomes important when the energy of a
ripplon involved compares with the collision broadening of Landau levels.
Usually, such a condition is realized only at sufficiently high magnetic
fields. On the contrary, the inelastic nature of inter-subband scattering is
shown to be more important in a lower magnetic field range because of the new
enhancement factor: the ratio of the inter-subband transition frequency to the
cyclotron frequency. This inelastic effect affects strongly the shape of
conductivity oscillations which acquires an additional wavy feature (a mixture
of splitting and inversion) in the vicinity of the level-matching points where
the above noted ratio is close to an integer.Comment: 10 pages 6 figure

### 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.Comment: 5 pages, 5 figure

### High-Frequency Properties of a Graphene Nanoribbon Field-Effect Transistor

We propose an analytical device model for a graphene nanoribbon field-effect
transistor (GNR-FET). The GNR-FET under consideration is based on a
heterostructure which consists of an array of nanoribbons clad between the
highly conducting substrate (the back gate) and the top gate controlling the dc
and ac source-drain currents. Using the model developed, we derive explicit
analytical formulas for the GNR-FET transconductance as a function of the
signal frequency, collision frequency of electrons, and the top gate length.
The transition from the ballistic and to strongly collisional electron
transport is considered.Comment: 7 pages, 7 figure

### Multiple and virtual photon processes in radiation-induced magnetoresistance oscillations in two-dimensional electron systems

Recently discovered new structures and zero-resistance states outside the
well-known oscillations are demonstrated to arise from multiphoton assisted
processes, by a detailed analysis of microwave photoresistance in
two-dimensional electron systems under enhanced radiation. The concomitant
resistance dropping and peak narrowing observed in the experiments are also
reproduced. We show that the radiation-induced suppression of average
resistance comes from virtual photon effect and exists throughout the whole
magnetic field range.Comment: 4 pages, 2 figures, published versio

### Microwave photoresponse in the 2D electron system caused by intra-Landau level transitions

The influence of microwave radiation on the DC-magnetoresistance of
2D-electrons is studied in the regime beyond the recently discovered zero
resistance states when the cyclotron frequency exceeds the radiation frequency.
Radiation below 30 GHz causes a strong suppression of the resistance over a
wide magnetic field range, whereas higher frequencies produce a non-monotonic
behavior in the damping of the Shubnikov-de Haas oscillations. These
observations are explained by the creation of a non-equilibrium electron
distribution function by microwave induced intra-Landau level transitions.Comment: 4 pages, 5 figure

### Phonon-induced resistance oscillations of two-dimensional electron systems drifting with supersonic velocities

We present a theory of the phonon-assisted nonlinear dc transport of 2D
electrons in high Landau levels. The nonlinear dissipative resistivity displays
quantum magneto-oscillations governed by two parameters which are proportional
to the Hall drift velocity $v_H$ of electrons in electric field and the speed
of sound $s$. In the subsonic regime, $v_H<s$, the theory quantitatively
reproduces the oscillation pattern observed in recent experiments. We also find
the $\pi/2$ phase change of oscillations across the sound barrier $v_H=s$. In
the supersonic regime, $v_H>s$, the amplitude of oscillations saturates with
lowering temperature, while the subsonic region displays exponential
suppression of the phonon-assisted oscillations with temperature.Comment: 4 pages, 3 figure

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