7,907 research outputs found
Reentrant nu = 1 quantum Hall state in a two-dimensional hole system
We report the observation of a reentrant quantum Hall state at the Landau
level filling factor nu = 1 in a two-dimensional hole system confined to a
35-nm-wide (001) GaAs quantum well. The reentrant behavior is characterized by
a weakening and eventual collapse of the nu = 1 quantum Hall state in the
presence of a parallel magnetic field component B||, followed by a
strengthening and reemergence as B|| is further increased. The robustness of
the nu = 1 quantum Hall state during the transition depends strongly on the
charge distribution symmetry of the quantum well, while the magnitude of B||
needed to invoke the transition increases with the total density of the system
Anisotropic Fermi Contour of (001) GaAs Holes in Parallel Magnetic Fields
We report a severe, spin-dependent, Fermi contour anisotropy induced by
parallel magnetic field in a high-mobility (001) GaAs two-dimensional hole
system. Employing commensurability oscillations created by a unidirectional,
surface-strain-induced, periodic potential modulation, we directly probe the
anisotropy of the two spin subband Fermi contours. Their areas are obtained
from the Fourier transform of the Shubnikov-de Haas oscillations. Our findings
are in semi-quantitative agreement with the results of parameter-free
calculations of the energy bands.Comment: 4 pages, 4 figure
Tuning of Fermi Contour Anisotropy in GaAs (001) 2D Holes via Strain
We demonstrate tuning of the Fermi contour anisotropy of two-dimensional (2D)
holes in a symmetric GaAs (001) quantum well via the application of in-plane
strain. The ballistic transport of high-mobility hole carriers allows us to
measure the Fermi wavevector of 2D holes via commensurability oscillations as a
function of strain. Our results show that a small amount of in-plane strain, on
the order of , can induce significant Fermi wavevector anisotropy as
large as 3.3, equivalent to a mass anisotropy of 11 in a parabolic band. Our
method to tune the anisotropy \textit{in situ} provides a platform to study the
role of anisotropy on phenomena such as the fractional quantum Hall effect and
composite fermions in interacting 2D systems.Comment: Accepted to Applied Physics Letter
Even-denominator Fractional Quantum Hall Effect at a Landau Level Crossing
The fractional quantum Hall effect (FQHE), observed in two-dimensional (2D)
charged particles at high magnetic fields, is one of the most fascinating,
macroscopic manifestations of a many-body state stabilized by the strong
Coulomb interaction. It occurs when the filling factor () of the quantized
Landau levels (LLs) is a fraction which, with very few exceptions, has an odd
denominator. In 2D systems with additional degrees of freedom it is possible to
cause a crossing of the LLs at the Fermi level. At and near these crossings,
the FQHE states are often weakened or destroyed. Here we report the observation
of an unusual crossing of the two \emph{lowest-energy} LLs in high-mobility
GaAs 2D systems which brings to life a new \emph{even-denominator} FQHE
at
Anisotropic Fermi Contour of (001) GaAs Electrons in Parallel Magnetic Fields
We demonstrate a severe Fermi contour anisotropy induced by the application
of a parallel magnetic field to high-mobility electrons confined to a
30-nm-wide (001) GaAs quantum well. We study commensurability oscillations,
namely geometrical resonances of the electron orbits with a unidirectional,
surface-strain-induced, periodic potential modulation, to directly probe the
size of the Fermi contours along and perpendicular to the parallel field. Their
areas are obtained from the Shubnikov-de Haas oscillations. Our experimental
data agree semi-quantitatively with the results of parameter-free calculations
of the Fermi contours but there are significant discrepancies.Comment: 5 pages, 5 figure
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