1,523 research outputs found
Interplay among spin, orbital effects and localization in a GaAs two-dimensional electron gas in a strong in-plane magnetic field
The magnetoresistance of a low carrier density, disordered GaAs based
two-dimensional (2D) electron gas has been measured in parallel magnetic fields
up to 32 T. The feature in the resistance associated with the complete spin
polarization of the carriers shifts down by more than 20 T as the electron
density is reduced, consistent with recent theories taking into account the
enhancement of the electron-electron interactions at low densities.
Nevertheless, the magnetic field for complete polarization, Bp, remains 2-3
times smaller than predicted for a disorder free system. We show, in particular
by studying the temperature dependance of Bp to probe the effective size of the
Fermi sea, that localization plays an important role in determining the spin
polarization of a 2D electron gas.Comment: Published in the Physical Review
Tuning Energy Relaxation along Quantum Hall Channels
The chiral edge channels in the quantum Hall regime are considered ideal
ballistic quantum channels, and have quantum information processing
potentialities. Here, we demonstrate experimentally, at filling factor 2, the
efficient tuning of the energy relaxation that limits quantum coherence and
permits the return toward equilibrium. Energy relaxation along an edge channel
is controllably enhanced by increasing its transmission toward a floating ohmic
contact, in quantitative agreement with predictions. Moreover, by forming a
closed inner edge channel loop, we freeze energy exchanges in the outer
channel. This result also elucidates the inelastic mechanisms at work at
filling factor 2, informing us in particular that those within the outer edge
channel are negligible.Comment: 8 pages including supplementary materia
Noise dephasing in the edge states of the Integer Quantum Hall regime
An electronic Mach Zehnder interferometer is used in the integer quantum hall
regime at filling factor 2, to study the dephasing of the interferences. This
is found to be induced by the electrical noise existing in the edge states
capacitively coupled to each others. Electrical shot noise created in one
channel leads to phase randomization in the other, which destroys the
interference pattern. These findings are extended to the dephasing induced by
thermal noise instead of shot noise: it explains the underlying mechanism
responsible for the finite temperature coherence time of the
edge states at filling factor 2, measured in a recent experiment. Finally, we
present here a theory of the dephasing based on Gaussian noise, which is found
in excellent agreement with our experimental results.Comment: ~4 pages, 4 figure
Finite bias visibility of the electronic Mach-Zehnder interferometer
We present an original statistical method to measure the visibility of
interferences in an electronic Mach-Zehnder interferometer in the presence of
low frequency fluctuations. The visibility presents a single side lobe
structure shown to result from a gaussian phase averaging whose variance is
quadratic with the bias. To reinforce our approach and validate our statistical
method, the same experiment is also realized with a stable sample. It exhibits
the same visibility behavior as the fluctuating one, indicating the intrinsic
character of finite bias phase averaging. In both samples, the dilution of the
impinging current reduces the variance of the gaussian distribution.Comment: 4 pages, 5 figure
Strong back-action of a linear circuit on a single electronic quantum channel
What are the quantum laws of electricity in mesoscopic circuits? This very
fundamental question has also direct implications for the quantum engineering
of nanoelectronic devices. Indeed, when a quantum coherent conductor is
inserted into a circuit, its transport properties are modified. In particular,
its conductance is reduced because of the circuit back-action. This phenomenon,
called environmental Coulomb blockade, results from the granularity of charge
transfers across the coherent conductor. Although extensively studied for a
tunnel junction in a linear circuit, it is only fully understood for arbitrary
short coherent conductors in the limit of small circuit impedances and small
conductance reduction. Here, we investigate experimentally the strong
back-action regime, with a conductance reduction of up to 90%. This is achieved
by embedding a single quantum channel of tunable transmission in an adjustable
on-chip circuit of impedance comparable to the resistance quantum
at microwave frequencies. The experiment reveals important deviations from
calculations performed in the weak back-action framework, and matches with
recent theoretical results. From these measurements, we propose a generalized
expression for the conductance of an arbitrary quantum channel embedded in a
linear circuit.Comment: 11 pages including supplementary information, to be published in
Nature Physic
Tuning decoherence with a voltage probe
We present an experiment where we tune the decoherence in a quantum
interferometer using one of the simplest object available in the physic of
quantum conductors : an ohmic contact. For that purpose, we designed an
electronic Mach-Zehnder interferometer which has one of its two arms connected
to an ohmic contact through a quantum point contact. At low temperature, we
observe quantum interference patterns with a visibility up to 57%. Increasing
the connection between one arm of the interferometer to the floating ohmic
contact, the voltage probe, reduces quantum interferences as it probes the
electron trajectory. This unique experimental realization of a voltage probe
works as a trivial which-path detector whose efficiency can be simply tuned by
a gate voltage
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