391 research outputs found
Possible evidence of a spontaneous spin-polarization in mesoscopic 2D electron systems
We have experimentally studied the non-equilibrium transport in low-density
clean 2D electron systems at mesoscopic length scales. At zero magnetic field
(B), a double-peak structure in the non-linear conductance was observed close
to the Fermi energy in the localized regime. From the behavior of these peaks
at non-zero B, we could associate them to the opposite spin states of the
system, indicating a spontaneous spin polarization at B = 0. Detailed
temperature and disorder dependence of the structure shows that such a
splitting is a ground state property of the low-density 2D systems.Comment: 7 pages, 5 figure
Distinguishing impurity concentrations in GaAs and AlGaAs, using very shallow undoped heterostructures
We demonstrate a method of making a very shallow, gateable, undoped
2-dimensional electron gas. We have developed a method of making very low
resistivity contacts to these structures and systematically studied the
evolution of the mobility as a function of the depth of the 2DEG (from 300nm to
30nm). We demonstrate a way of extracting quantitative information about the
background impurity concentration in GaAs and AlGaAs, the interface roughness
and the charge in the surface states from the data. This information is very
useful from the perspective of molecular beam epitaxy (MBE) growth. It is
difficult to fabricate such shallow high-mobility 2DEGs using modulation doping
due to the need to have a large enough spacer layer to reduce scattering and
switching noise from remote ionsied dopants.Comment: 4 pages, 5 eps figure
Surface-acoustic-wave driven planar light-emitting device
Electroluminescence emission controlled by means of surface acoustic waves
(SAWs) in planar light-emitting diodes (pLEDs) is demonstrated. Interdigital
transducers for SAW generation were integrated onto pLEDs fabricated following
the scheme which we have recently developed. Current-voltage, light-voltage and
photoluminescence characteristics are presented at cryogenic temperatures. We
argue that this scheme represents a valuable building block for advanced
optoelectronic architectures
Magnetic Field Induced Instabilities in Localised Two-Dimensional Electron Systems
We report density dependent instabilities in the localised regime of
mesoscopic two-dimensional electron systems (2DES) with intermediate strength
of background disorder. They are manifested by strong resistance oscillations
induced by high perpendicular magnetic fields B_{\perp}. While the amplitude of
the oscillations is strongly enhanced with increasing B_{\perp}, their position
in density remains unaffected. The observation is accompanied by an unusual
behaviour of the temperature dependence of resistance and activation energies.
We suggest the interplay between a strongly interacting electron phase and the
background disorder as a possible explanation.Comment: 5 pages, 4 figure
Possible effect of collective modes in zero magnetic field transport in an electron-hole bilayer
We report single layer resistivities of 2-dimensional electron and hole gases
in an electron-hole bilayer with a 10nm barrier. In a regime where the
interlayer interaction is stronger than the intralayer interaction, we find
that an insulating state () emerges at or
lower, when both the layers are simultaneously present. This happens deep in
the metallic" regime, even in layers with , thus making
conventional mechanisms of localisation due to disorder improbable. We suggest
that this insulating state may be due to a charge density wave phase, as has
been expected in electron-hole bilayers from the Singwi-Tosi-Land-Sj\"olander
approximation based calculations of L. Liu {\it et al} [{\em Phys. Rev. B},
{\bf 53}, 7923 (1996)]. Our results are also in qualitative agreement with
recent Path-Integral-Monte-Carlo simulations of a two component plasma in the
low temperature regime [ P. Ludwig {\it et al}. {\em Contrib. Plasma Physics}
{\bf 47}, No. 4-5, 335 (2007)]Comment: 5 pages + 3 EPS figures (replaced with published version
Quantized charge pumping through a quantum dot by surface acoustic waves
We present a realization of quantized charge pumping. A lateral quantum dot
is defined by metallic split gates in a GaAs/AlGaAs heterostructure. A surface
acoustic wave whose wavelength is twice the dot length is used to pump single
electrons through the dot at a frequency f=3GHz. The pumped current shows a
regular pattern of quantization at values I=nef over a range of gate voltage
and wave amplitude settings. The observed values of n, the number of electrons
transported per wave cycle, are determined by the number of electronic states
in the quantum dot brought into resonance with the fermi level of the electron
reservoirs during the pumping cycle.Comment: 8 page
Acoustic charge transport in n-i-n three terminal device
We present an unconventional approach to realize acoustic charge transport
devices that takes advantage from an original input region geometry in place of
standard Ohmic input contacts. Our scheme is based on a n-i-n lateral junction
as electron injector, an etched intrinsic channel, a standard Ohmic output
contact and a pair of in-plane gates. We show that surface acoustic waves are
able to pick up electrons from a current flowing through the n-i-n junction and
steer them toward the output contact. Acoustic charge transport was studied as
a function of the injector current and bias, the SAW power and at various
temperatures. The possibility to modulate the acoustoelectric current by means
of lateral in-plane gates is also discussed. The main advantage of our approach
relies on the possibility to drive the n-i-n injector by means of both voltage
or current sources, thus allowing to sample and process voltage and current
signals as well.Comment: 9 pages, 3 figures. Submitted to Applied Physics Letter
Theory of the in-plane photoelectric effect in a two-dimensional electron system
A new photoelectric phenomenon, the in-plane photoelectric (IPPE) effect, has
been recently discovered at terahertz (THz) frequencies in a
GaAs/AlGaAs heterostructure with a two-dimensional (2D) electron
gas (W. Michailow et al., Science Advances, DOI: 10.1126/sciadv.abi8398). In
contrast to the conventional PE phenomena, the IPPE effect is observed at
normal incidence of radiation, the height of the in-plane potential step, which
electrons overcome after absorption of a THz photon, is electrically tunable by
gate voltages, and the effect is maximal at a negative electron "work
function", when the Fermi energy lies above the potential barrier. Based on the
discovered phenomenon, efficient detection of THz radiation has been
demonstrated. In this work we present a detailed theory of the IPPE effect
providing analytical results for the THz wave generated photocurrent, the
quantum efficiency, and the internal responsivity of the detector, in
dependence on the frequency, the gate voltages, and the geometrical parameters
of the detector. The calculations are performed for macroscopically wide
samples at zero temperature. Results of the theory are applicable to any
semiconductor systems with 2D electron gases, including III-V structures,
silicon-based field effect transistors, and the novel 2D layered,
graphene-related materials.Comment: 21 pages, 15 figures, substantially revised improved versio
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