100 research outputs found
Role of finite layer thickness in spin-polarization of GaAs 2D electrons in strong parallel magnetic fields
We report measurements and calculations of the spin-polarization, induced by
a parallel magnetic field, of interacting, dilute, two-dimensional electron
systems confined to GaAs/AlGaAs heterostructures. The results reveal the
crucial role the non-zero electron layer thickness plays: it causes a
deformation of the energy surface in the presence of a parallel field, leading
to enhanced values for the effective mass and g-factor and a non-linear
spin-polarization with field.Comment: 4 pages, 4 figures, Fig. 4 has been replaced from the previous
version, minor changes in the tex
Negative differential Rashba effect in two-dimensional hole systems
We demonstrate experimentally and theoretically that two-dimensional (2D)
heavy hole systems in single heterostructures exhibit a \emph{decrease} in
spin-orbit interaction-induced spin splitting with an increase in perpendicular
electric field. Using front and back gates, we measure the spin splitting as a
function of applied electric field while keeping the density constant. Our
results are in contrast to the more familiar case of 2D electrons where spin
splitting increases with electric field.Comment: 3 pages, 3 figures. To appear in AP
Structural and electrical characterization of hybrid metal-polypyrrole nanowires
We present here the synthesis and structural characterization of hybrid
Au-polypyrrole-Au and Pt- polypyrrole-Au nanowires together with a study of
their electrical properties from room-temperature down to very low temperature.
A careful characterization of the metal-polymer interfaces by trans- mission
electron microscopy revealed that the structure and mechanical strength of
bottom and upper interfaces are very different. Variable temperature electrical
transport measurements were performed on both multiple nanowires - contained
within the polycarbonate template - and single nanowires. Our data show that
the three-dimensional Mott variable-range-hopping model provides a complete
framework for the understanding of transport in PPy nanowires, including
non-linear current-voltage characteristics and magnetotransport at low
temperatures.Comment: Phys. Rev. B Vol. 76 Issue 11 (2007
Anomalous Spin Polarization of GaAs Two-Dimensional Hole Systems
We report measurements and calculations of the spin-subband depopulation,
induced by a parallel magnetic field, of dilute GaAs two-dimensional (2D) hole
systems. The results reveal that the shape of the confining potential
dramatically affects the values of in-plane magnetic field at which the upper
spin subband is depopulated. Most surprisingly, unlike 2D electron systems, the
carrier-carrier interaction in 2D hole systems does not significantly enhance
the spin susceptibility. We interpret our findings using a multipole expansion
of the spin density matrix, and suggest that the suppression of the enhancement
is related to the holes' band structure and effective spin j=3/2.Comment: 6 pages, 4 figures, substantially extended discussion of result
Observation of a new phase transition between fully and partially polarized quantum Hall states with charge and spin gaps at
The average electron spin-polarization of two-dimensional electron
gas confined in multiple quantum-wells was measured by
nuclear magnetic resonance (NMR) near the fractional quantum Hall state with
filling factor . Above this filling factor (), a strong depolarization is observed corresponding to two spin flips per
additional flux quantum. The most remarkable behavior of the polarization is
observed at , where a quantum phase transition from a partially
polarized () to a fully polarized ()
state can be driven by increasing the ratio between the Zeeman and the Coulomb
energy above a critical value .Comment: 4 pages including 4 figure
Thermopower of Interacting GaAs Bilayer Hole Systems in the Reentrant Insulating Phase near
We report thermopower measurements of interacting GaAs bilayer hole systems.
When the carrier densities in the two layers are equal, these systems exhibit a
reentrant insulating phase near the quantum Hall state at total filling factor
. Our data show that as the temperature is decreased, the thermopower
diverges in the insulating phase. This behavior indicates the opening of an
energy gap at low temperature, consistent with the formation of a pinned Wigner
solid. We extract an energy gap and a Wigner solid melting phase diagram.Comment: to be published in Phys. Rev. Let
Layer charge instability in unbalanced bilayer systems in the quantum Hall regime
Measurements in GaAs hole bilayers with unequal layer densities reveal a
pronounced magneto-resistance hysteresis at the magnetic field positions where
either the majority or minority layer is at Landau level filling factor one. At
a fixed field in the hysteretic regions, the resistance exhibits an unusual
time dependence, consisting of random, bidirectional jumps followed by slow
relaxations. These anomalies are apparently caused by instabilities in the
charge distribution of the two layers.Comment: 4 pages, 4 figure
NMR Determination of 2D Electron Spin Polarization at
Using a `standard' NMR spin-echo technique we determined the spin
polarization of two-dimensional electrons, confined to GaAs quantum wells, from
the hyperfine shift of Ga nuclei in the wells. Concentrating on the temperature
and magnetic field dependencies of spin polarization at Landau level filling
factor , we find that the results are described well by a simple
model of non-interacting composite fermions, although some inconsistencies
remain when the two-dimensional electron system is tilted in the magnetic
field.Comment: 4 pages (REVTEX) AND 4 figures (PS
A Laterally Modulated 2D Electron System in the Extreme Quantum Limit
We report on magnetotransport of a two-dimensional electron system (2DES),
located 32 nm below the surface, with a surface superlattice gate structure of
periodicity 39 nm imposing a periodic modulation of its potential. For low
Landau level fillings , the diagonal resistivity displays a rich pattern
of fluctuations, even though the disorder dominates over the periodic
modulation. Theoretical arguments based on the combined effects of the
long-wavelength, strong disorder and the short-wavelength, weak periodic
modulation present in the 2DES qualitatively explain the data.Comment: 4 pages, 5 figures. to appear in Phys. Rev. Let
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