278 research outputs found
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
Microwave induced magnetoresistance oscillations at the subharmonics of the cyclotron resonance
The magnetoresistance oscillations, which occur in a two-dimensional electron
system exposed to strong microwave radiation when the microwave frequency
coincides with the n-th subharmonic of the cyclotron frequency
have been investigated for n = 2, 3 and 4. It is shown that these
subharmonic features can be explained within a non-equilibrium energy
distribution function picture without invoking multi-photon absorption
processes. The existence of a frequency threshold above which such oscillations
disappear lends further support to this explanation.Comment: 5 pages, 5 figure
Nonlinear theory of fractional microwave-induced magnetoresistance oscillations in a dc-driven two-dimensional electron system
Microwave-induced nonlinear magnetoresistance in a dc-driven two-dimensional
electron system is examined using a multi-photon-assisted transport scheme
direct controlled by the current. It is shown that near the 2nd subharmonic of
the cyclotron resonance, the frequency of the resistivity oscillation with the
magnetic-field-normalized current-density is double that at the cyclotron
resonance and its harmonics, in excellent agreement with recent experimental
findings by Hatke {\it et al.} [Phys. Rev. Lett. {\bf 101}, 246811 (2008)]. The
current-induced alternative emergence of resonant two-photon and single-photon
processes is responsible for this frequency doubling. Near the third
subharmonic of the cyclotron resonance, the current-induced consecutive
appearance of resonant 0-/3-photon, two-photon, and single-photon processes may
lead to the frequency tripling of the resistivity oscillation.Comment: 6 pages, 2 figures, published versio
Spin-orbit-induced correlations of the local density of states in two-dimensional electron gas
We study the local density of states (LDOS) of two-dimensional electrons in
the presence of spin-orbit (SO) coupling. Although SO coupling has no effect on
the average density of states, it manifests itself in the correlations of the
LDOS. Namely, the correlation function acquires two satellites centered at
energy difference equal to the SO splitting, , of the electron
Fermi surface. For a smooth disorder the satellites are well separated from the
main peak. Weak Zeeman splitting in a parallel
magnetic field causes an anomaly in the shape of the satellites. We consider
the effect of SO-induced satellites in the LDOS correlations on the shape of
the correlation function of resonant-tunneling conductances at different
source-drain biases, which can be measured experimentally. This shape is
strongly sensitive to the relation between and .Comment: 10 pages, 4 figure
Photon-assisted scattering and magnetoconductivity oscillations in a strongly correlated 2D electron system formed on the surface of liquid helium
The influence of strong internal forces on photon-assisted scattering and on
the displacement mechanism of magnetoconductivity oscillations in a
two-dimensional (2D) electron gas is theoretically studied. The theory is
applied to the highly correlated system of surface electrons on liquid helium
under conditions that the microwave frequency is substantially different from
inter-subband resonance frequencies. A strong dependence of the amplitude of
magnetoconductivity oscillations on the electron density is established. The
possibility of experimental observation of such oscillations caused by
photon-assisted scattering is discussed.Comment: 7 pages, 1 figur
Giant Magnetoresistance Oscillations Induced by Microwave Radiation and a Zero-Resistance State in a 2D Electron System with a Moderate Mobility
The effect of a microwave field in the frequency range from 54 to 140
on the magnetotransport in a GaAs quantum well with AlAs/GaAs
superlattice barriers and with an electron mobility no higher than
is investigated. In the given two-dimensional system under
the effect of microwave radiation, giant resistance oscillations are observed
with their positions in magnetic field being determined by the ratio of the
radiation frequency to the cyclotron frequency. Earlier, such oscillations had
only been observed in GaAs/AlGaAs heterostructures with much higher mobilities.
When the samples under study are irradiated with a 140- microwave
field, the resistance corresponding to the main oscillation minimum, which
occurs near the cyclotron resonance, appears to be close to zero. The results
of the study suggest that a mobility value lower than
does not prevent the formation of zero-resistance states in magnetic field in a
two-dimensional system under the effect of microwave radiation.Comment: 4 pages, 2 figur
Application of planetary ball mill for manufacturing of shielding composite coatings based on polyester powder paints and carbon fillers
Blend polyester powder paint and particulate carbon filler in the form of colloidal graphite and the carbon black product were investigated. Powder paint and carbon materials were treated together in a planetary ball mill. The data of the structural analysis and transmission coefficients of electromagnetic waves of terahertz range through the flat shape samples are presented
Direct measurements of the fractional quantum Hall effect gaps
We measure the chemical potential jump across the fractional gap in the
low-temperature limit in the two-dimensional electron system of GaAs/AlGaAs
single heterojunctions. In the fully spin-polarized regime, the gap for filling
factor nu=1/3 increases LINEARLY with magnetic field and is coincident with
that for nu=2/3, reflecting the electron-hole symmetry in the spin-split Landau
level. In low magnetic fields, at the ground-state spin transition for nu=2/3,
a correlated behavior of the nu=1/3 and nu=2/3 gaps is observed
The foam-glass material for a radio frequency echoless chambers
The conducted experiment of foam glass modification by carbon nanotubes shows increased radio absorbing properties in comparison with a foam glass without additives. Addition of carbon nanodimensional tubes in number of 1,5 wt.% increases a tangent of dielectric losses angle by 2,5 times. The coefficient of electromagnetic radiation absorption in the range of frequencies of 120 - 260 GHz increases for a foam glass with carbon nanotubes (1,5 wt. %) twice in comparison with a foam glass without additives. The foam glass modified by carbon nanotubes is recommended as the effective radio absorbing material for the device of anechoic cameras. This material is fire safety, nonflammable, environmentally friendly, rather light-weight
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