407 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
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
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
Single-electron pump with highly controllable plateaus
Future quantum based electronic systems will demand robust and highly accurate on-demand sources of current. The ultimate limit of quantized current sources is a highly controllable device that manipulates individual electrons. We present a GaAs single-electron pump, where electrons are pumped through a one-dimensional split-gate saddle point confinement potential, which show quantized plateaus with length and width that can be independently tuned with the application of a source-drain bias and RF amplitude. The plateaus can be over two orders of magnitude longer than conventional pumps, and flatness improves with the application of a source-drain bias
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
Nuclear spin coherence in a quantum wire
We have observed millisecond-long coherent evolution of nuclear spins in a
quantum wire at 1.2 K. Local, all-electrical manipulation of nuclear spins is
achieved by dynamic nuclear polarization in the breakdown regime of the Integer
Quantum Hall Effect combined with pulsed Nuclear Magnetic Resonance. The
excitation thresholds for the breakdown are significantly smaller than what
would be expected for our sample and the direction of the nuclear polarization
can be controlled by the voltage bias. As a four-level spin system, the device
is equivalent to two qubits.Comment: 5 pages, 5 figure
Surface acoustic wave-induced electroluminescence intensity oscillation in planar light-emitting devices
Electroluminescence emission from surface acoustic wave-driven light-emitting
diodes (SAWLEDs) is studied by means of time-resolved techniques. We show that
the intensity of the SAW-induced electroluminescence is modulated at the SAW
frequency (~1 GHz), demonstrating electron injection into the p-type region
synchronous with the SAW wavefronts.Comment: 4 pages, 3 figure
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