453 research outputs found
A quantum Hall Mach-Zehnder interferometer far beyond the equilibrium
We experimentally realize quantum Hall Mach-Zehnder interferometer which
operates far beyond the equilibrium. The operation of the interferometer is
based on allowed intra-edge elastic transitions within the same Landau sublevel
in the regime of high imbalances between the co-propagating edge states. Since
the every edge state is definitely connected with the certain Landau sublevel,
the formation of the interference loop can be understood as a splitting and a
further reconnection of a single edge state. We observe an Aharonov-Bohm type
interference pattern even for low-size interferometers. This novel interference
scheme demonstrates high visibility even at millivolt imbalances and survives
in a wide temperature range.Comment: As accepted by PR
Waveform sampling using an adiabatically driven electron ratchet in a two-dimensional electron system
We utilize a time-periodic ratchet-like potential modulation imposed onto a
two-dimensional electron system inside a GaAs/AlGaAs
heterostructure to evoke a net dc pumping current. The modulation is induced by
two sets of interdigitated gates, interlacing off center, which can be
independently addressed. When the transducers are driven by two identical but
phase-shifted ac signals, a lateral dc pumping current results, which
strongly depends on both, the phase shift and the waveform of the
imposed gate voltages. We find that for different periodic signals, the phase
dependence closely resembles . A simple linear model of
adiabatic pumping in two-dimensional electron systems is presented, which
reproduces well our experimental findings.Comment: 3 figure
Electrical read-out of the local nuclear polarization in the quantum Hall effect
It is demonstrated that the now well-established `flip-flop' mechanism of
spin exchange between electrons and nuclei in the quantum Hall effect can be
reversed. We use a sample geometry which utilizes separately contacted edge
states to establish a local nuclear spin polarization --close to the maximum
value achievable-- by driving a current between electron states of different
spin orientation. When the externally applied current is switched off, the
sample exhibits an output voltage of up to a few tenths of a meV, which decays
with a time constant typical for the nuclear spin relaxation. The surprizing
fact that a sample with a local nuclear spin polarization can act as a source
of energy and that this energy is well above the nuclear Zeeman splitting is
explained by a simple model which takes into account the effect of a local
Overhauser shift on the edge state reconstruction.Comment: Submitted to Phys. Rev. Let
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