431 research outputs found
Interlayer tunneling in counterflow experiments on the excitonic condensate in quantum Hall bilayers
The effect of tunneling on the transport properties of} quantum Hall double
layers in the regime of the excitonic condensate at total filling factor one is
studied in counterflow experiments. If the tunnel current is smaller than a
critical , tunneling is large and is effectively shorting the two layers.
For tunneling becomes negligible. Surprisingly, the transition
between the two tunneling regimes has only a minor impact on the features of
the filling-factor one state as observed in magneto-transport, but at currents
exceeding the resistance along the layers increases rapidly
Quantum Hall Effect in a Two-Dimensional Electron System Bent by 90 Degrees
Using a new MBE growth technique, we fabricate a two-dimensional electron
system which is bent around an atomically sharp 90 degree corner. In the
quantum Hall regime under tilted magnetic fields, we can measure equilibration
between both co- and counter-propagating edge channels of arbitrary filling
factor ratio. We present here 4-point magnetotransport characterization of the
corner junction with filling factor combinations which can all be explained
using the standard Landauer-Buttiker edge channel picture. The success of this
description confirms the realization of a new type of quantum Hall edge
geometry.Comment: 4 pages, figures included Typographical errors corrected, reference
adde
Renormalization Group Derivation of the Localization Length Exponent in the Integer Quantum Hall Effect
We compute, neglecting possible effects of subleading irrelevant couplings,
the localization length exponent in the integer quantum Hall effect, for the
case of white noise random potentials. The result obtained is for all
Landau levels. Our approach consists in a renormalization group transformation
of Landau orbitals, which iterates the generating functional of Green's
functions for the localization problem. The value of is obtained from the
asymptotic form of the renormalization group mapping. The basic assumptions in
our derivation are the existence of a scaling law for the localization length
and the absence of Landau level mixing.Comment: Computations are discussed in a more detailed wa
The Cyclotron Spin-Flip Mode as the Lowest-Energy Excitation of Unpolarized Integer Quantum Hall States
The cyclotron spin-flip modes of spin unpolarized integer quantum Hall states
() have been studied with inelastic light scattering. The energy of
these modes is significantly smaller compared to the bare cyclotron gap. Second
order exchange corrections are held responsible for a negative energy
contribution and render these modes the lowest energy excitations of
unpolarized integer quantum Hall states.Comment: Published: Phys. Rev. B 72, 073304 (2005
Shape oscillations in non-degenerate Bose gases - transition from the collisionless to the hydrodynamic regime
We investigate collective oscillations of non-degenerate clouds of Rb-87
atoms as a function of density in an elongated magnetic trap. For the low-lying
M=0 monopole-quadrupole shape oscillation we measure the oscillation
frequencies and damping rates. At the highest densities the mean-free-path is
smaller than the axial dimension of the sample, which corresponds to
collisionally hydrodynamic conditions. This allows us to cover the cross-over
from the collisionless to the hydrodynamic regime. The experimental results
show good agreement with theory. We also analyze the influence of trap
anharmonicities on the oscillations in relation to observed temperature
dependencies of the dipole and quadrupole oscillation frequencies. We present
convenient expressions to quantify these effects.Comment: 10 pages, 5 figure
Exciton condensate at a total filling factor of 1 in Corbino 2D electron bilayers
Magneto-transport and drag measurements on a quasi-Corbino 2D electron
bilayer at the systems total filling factor 1 (v_tot=1) reveal a drag voltage
that is equal in magnitude to the drive voltage as soon as the two layers begin
to form the expected v_tot=1 exciton condensate. The identity of both voltages
remains present even at elevated temperatures of 0.25 K. The conductance in the
current carrying layer vanishes only in the limit of strong coupling between
the two layers and at T->0 K which suggests the presence of an excitonic
circular current
Precision of Quantization of the Hall Conductivity in a Sample of Finite Size: Power Law
A microscopic calculation of the conductivity in the integer quantum Hall
effect (IQHE) regime is carried out. The problem of precision of quantization
is analyzed for samples of finite size. It is demonstrated that the precision
of quantization shows a power-law dependence on the sample size. A new scaling
parameter describing a dependence of this kind is introduced. It is also
demonstrated that the precision of quantization linearly depends on the ratio
between the amplitude of the chaotic potential and the cyclotron energy. The
results obtained are compared with the magnetotransport measurements in
mesoscopic samples.Comment: 5 pages, 4 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
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