176 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
Acoustic Measurements of the Stripe and the Bubble Quantum Hall Phases
We launch surface acoustic waves (SAW) along both the directions of a Hall bar and measure the anisotropic conductivity
in a high purity GaAs 2-D electron system in the Quantum Hall regime of the
stripe and the bubble phases. In the anisotropic stripe phase, SAW propagating
along the "easy" direction. In the isotropic bubble phase,
the SAW data show compressible behavior in both directions, in marked contrast
to the incompressible quantum Hall behavior seen in transport measurements.
These results challenge models that assume that both the stripe and the bubble
phase consist of incompressible domains and raise important questions about the
role of domain boundaries in SAW propagation.Comment: Published version from New Journal of Physic
Electron spin resonance on a 2-dimensional electron gas in a single AlAs quantum well
Direct electron spin resonance (ESR) on a high mobility two dimensional
electron gas in a single AlAs quantum well reveals an electronic -factor of
1.991 at 9.35 GHz and 1.989 at 34 GHz with a minimum linewidth of 7 Gauss. The
ESR amplitude and its temperature dependence suggest that the signal originates
from the effective magnetic field caused by the spin orbit-interaction and a
modulation of the electron wavevector caused by the microwave electric field.
This contrasts markedly to conventional ESR that detects through the microwave
magnetic field.Comment: 4 pages, 4 figure
Coulomb Drag as a Probe of the Nature of Compressible States in a Magnetic Field
Magneto-drag reveals the nature of compressible states and the underlying
interplay of disorder and interactions. At \nu=3/2 a clear T^{4/3} dependence
is observed, which signifies the metallic nature of the N=0 Landau level. In
contrast, drag in higher Landau levels reveals an additional contribution,
which anomalously grows with decreasing T before turning to zero following a
thermal activation law. The anomalous drag is discussed in terms of
electron-hole asymmetry arising from disorder and localization, and the
crossover to normal drag at high fields as due to screening of disorder.Comment: 5 pages, 4 figure
Josephson-like tunnel resonance and large Coulomb drag in GaAs-based electron-hole bilayers
Bilayers consisting of two-dimensional (2D) electron and hole gases separated
by a 10 nm thick AlGaAs barrier are formed by charge accumulation in
epitaxially grown GaAs. Both vertical and lateral electric transport are
measured in the millikelvin temperature range. The conductivity between the
layers shows a sharp tunnel resonance at a density of , which is consistent with a Josephson-like enhanced tunnel
conductance. The tunnel resonance disappears with increasing densities and the
two 2D charge gases start to show 2D-Fermi-gas behavior. Interlayer
interactions persist causing a positive drag voltage that is very large at
small densities. The transition from the Josephson-like tunnel resonance to the
Fermi-gas behavior is interpreted as a phase transition from an exciton gas in
the Bose-Einstein-condensate state to a degenerate electron-hole Fermi gas
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