11,635 research outputs found
Field-induced resonant tunneling between parallel two-dimensional electron systems
Resonant tunneling between two high-mobility two-dimensional (2D) electron systems in a double quantum well structure has been induced by the action of an external Schottky gate field. Using one 2D electron gas as source and the other as drain, the tunnel conductance between them shows a strong resonance when the gate field aligns the ground subband edges of the two quantum wells
Independently contacted two-dimensional electron systems in double quantum wells
A new technique for creating independent ohmic contacts to closely spaced two-dimensional electron systems in double quantum well (DQW) structures is described. Without use of shallow diffusion or precisely controlled etching methods, the present technique results in low-resistance contacts which can be electrostatically switched between the two-conducting layers. The method is demonstrated with a DQW consisting of two 200 Ã… GaAs quantum wells separated by a 175 Ã… AlGaAs barrier. A wide variety of experiments on Coulomb and tunnel-coupled 2D electron systems is now accessible
Charge metastability and hysteresis in the quantum Hall regime
We report simultaneous quasi-dc magnetotransport and high frequency surface
acoustic wave measurements on bilayer two-dimensional electron systems in GaAs.
Near strong integer quantized Hall states a strong magnetic field sweep
hysteresis in the velocity of the acoustic waves is observed at low
temperatures. This hysteresis indicates the presence of a metastable state with
anomalously high conductivity in the interior of the sample. This
non-equilibrium state is not revealed by conventional low frequency transport
measurements which are dominated by dissipationless transport at the edge of
the 2D system. We find that a field-cooling technique allows the equilibrium
charge configuration within the interior of the sample to be established. A
simple model for this behavior is discussed.Comment: 8 pages, 4 postscript figure
Metastable Resistance Anisotropy Orientation of Two-Dimensional Electrons in High Landau Levels
In half-filled high Landau levels, two-dimensional electron systems possess
collective phases which exhibit a strongly anisotropic resistivity tensor. A
weak, but as yet unknown, rotational symmetry-breaking potential native to the
host semiconductor structure is necessary to orient these phases in macroscopic
samples. Making use of the known external symmetry-breaking effect of an
in-plane magnetic field, we find that the native potential can have two
orthogonal local minima. It is possible to initialize the system in the higher
minimum and then observe its relaxation toward equilibrium.Comment: 5 pages, 3 figures. Figure references corrected. Version accepted for
publication in Physical Review Letter
Quantum Hall Exciton Condensation at Full Spin Polarization
Using Coulomb drag as a probe, we explore the excitonic phase transition in
quantum Hall bilayers at nu=1 as a function of Zeeman energy, E_Z. The critical
layer separation d/l for exciton condensation initially increases rapidly with
E_Z, but then reaches a maximum and begins a gentle decline. At high E_Z, where
both the excitonic phase at small d/l and the compressible phase at large d/l
are fully spin polarized, we find that the width of the transition, as a
function of d/l, is much larger than at small E_Z and persists in the limit of
zero temperature. We discuss these results in the context of two models in
which the system contains a mixture of the two fluids.Comment: 4 pages, 3 eps figure
Quantum Hall Exciton Condensation at Full Spin Polarization
Using Coulomb drag as a probe, we explore the excitonic phase transition in quantum Hall bilayers at ν_T = 1 as a function of Zeeman energy E_Z. The critical layer separation (d/ℓ)_c for exciton condensation initially increases rapidly with E_Z, but then reaches a maximum and begins a gentle decline. At high E_Z, where both the excitonic phase at small d/ℓ and the compressible phase at large d/ℓ are fully spin polarized, we find that the width of the transition, as a function of d/ℓ, is much larger than at small E_Z and persists in the limit of zero temperature. We discuss these results in the context of two models in which the system contains a mixture of the two fluids
Exciton Transport and Andreev Reflection in a Bilayer Quantum Hall System
We demonstrate that counterflowing electrical currents can move through the bulk of the excitonic quantized Hall phase found in bilayer two-dimensional electron systems (2DES) even as charged excitations cannot. These counterflowing currents are transported by neutral excitons which are emitted and absorbed at the inner and outer boundaries of an annular 2DES via Andreev reflection
Bilayer Quantum Hall Systems at nuT = 1: Coulomb Drag and the Transition from Weak to Strong Interlayer Coupling
Measurements revealing anomalously large frictional drag at the transition between the weakly and strongly coupled regimes of a bilayer two-dimensional electron system at total Landau level filling factor nuT = 1 are reported. This result suggests the existence of fluctuations, either static or dynamic, near the phase boundary separating the quantized Hall state at small layer separations from the compressible state at larger separations. Interestingly, the anomalies in drag seem to persist to larger layer separations than does interlayer phase coherence as detected in tunneling
- …