2,667 research outputs found
Magnetic Field Induced Insulating Phases at Large
Exploring a backgated low density two-dimensional hole sample in the large
regime we found a surprisingly rich phase diagram. At the highest
densities, beside the , 2/3, and 2/5 fractional quantum Hall states,
we observe both of the previously reported high field insulating and reentrant
insulating phases. As the density is lowered, the reentrant insulating phase
initially strengthens, then it unexpectedly starts weakening until it
completely dissapears. At the lowest densities the terminal quantum Hall state
moves from to . The intricate behavior of the insulating
phases can be explained by a non-monotonic melting line in the -
phase space
Reorientation of Anisotropy in a Square Well Quantum Hall Sample
We have measured magnetotransport at half-filled high Landau levels in a
quantum well with two occupied electric subbands. We find resistivities that
are {\em isotropic} in perpendicular magnetic field but become strongly {\em
anisotropic} at = 9/2 and 11/2 on tilting the field. The anisotropy
appears at an in-plane field, 2.5T, with the easy-current
direction {\em parallel} to but rotates by 90 at 10T and points now in the same direction as in single-subband samples.
This complex behavior is in quantitative agreement with theoretical
calculations based on a unidirectional charge density wave state model.Comment: 4 pages, 4 figure
Normal and Pathological NCAT Image and Phantom Data Based on Physiologically Realistic Left Ventricle Finite-Element Models
Electron correlation in the second Landau level; a competition between many, nearly degenerate quantum phases
At a very low temperature of 9mK, electrons in the 2nd Landau level of an
extremely high mobility two-dimensional electron system exhibit a very complex
electronic behavior. With varying filling factor, quantum liquids of different
origins compete with several insulating phases leading to an irregular pattern
in the transport parameters. We observe a fully developed state
separated from the even-denominator state by an insulating phase
and a and state surrounded by such phases. A developing
plateau at points to the existence of other even-denominator
states
Experimental studies of the fractional quantum Hall effect in the first excited Landau level
We present a spectrum of experimental data on the fractional quantum Hall
effect (FQHE) states in the first excited Landau level, obtained in an
ultrahigh mobility two-dimensional electron system (2DES) and at very low
temperatures and report the following results: For the even-denominator FQHE
states, the sample dependence of the nu=5/2 state clearly shows that disorder
plays an important role in determining the energy gap at nu=5/2. For the
developing nu=19/8 FQHE state the temperature dependence of the Rxx minimum
implies an energy gap of ~5mK.The energy gaps of the odd-denominator FQHE
states at nu=7/3 and 8/3 also increase with decreasing disorder, similar to the
gap at 5/2 state. Unexpectedly and contrary to earlier data on lower mobility
samples, in this ultra-high quality specimen, the nu=13/5 state is missing,
while its particle-hole conjugate state, the nu=12/5 state, is a fully
developed FQHE state. We speculate that this disappearance might indicate a
spin polarization of the nu=13/5 state. Finally, the temperature dependence is
studied for the two-reentrant integer quantum Hall states around nu=5/2 and is
found to show a very narrow temperature range for the transition from quantized
to classical value.Comment: to be publishe
High Magnetic Field Microwave Conductivity of 2D Electrons in an Array of Antidots
We measure the high magnetic field () microwave conductivity,
Re, of a high mobility 2D electron system containing an antidot
array. Re vs frequency () increases strongly in the regime of
the fractional quantum Hall effect series, with Landau filling .
At microwave , Re vs exhibits a broad peak centered around
. On the peak, the 10 GHz Re can exceed its dc-limit
value by a factor of 5. This enhanced microwave conductivity is unobservable
for temperature K, and grows more pronounced as is
decreased. The effect may be due to excitations supported by the antidot edges,
but different from the well-known edge magnetoplasmons.Comment: 4 pages, 3 figures, revtex
Magnetic von-Neumann lattice for two-dimensional electrons in the magnetic field
One-particle eigenstates and eigenvalues of two-dimensional electrons in the
strong magnetic field with short range impurity and impurities, cosine
potential, boundary potential, and periodic array of short range potentials are
obtained by magnetic von-Neumann lattice in which Landau level wave functions
have minimum spatial extensions. We find that there is a dual correspondence
between cosine potential and lattice kinetic term and that the representation
based on the von-Neumann lattice is quite useful for solving the system's
dynamics.Comment: 21pages, figures not included, EPHOU-94-00
Josephson Plasma Resonance as a Structural Probe of Vortex Liquid
Recent developments of the Josephson plasma resonance and transport c-axis
measurements in layered high T superconductors allow to probe Josephson
coupling in a wide range of the vortex phase diagram. We derive a relation
between the field dependent Josephson coupling energy and the density
correlation function of the vortex liquid. This relation provides a unique
opportunity to extract the density correlation function of pancake vortices
from the dependence of the plasma resonance on the -component of the
magnetic field at a fixed -axis component.Comment: 4 pages, 1 fugure, accepted to Phys. Rev. Let
Experimental evidence for the formation of stripe phases in Si/SiGe
We observe pronounced transport anisotropies in magneto-transport experiments
performed in the two-dimensional electron system of a Si/SiGe heterostructure.
They occur when an in-plane field is used to tune two Landau levels with
opposite spin to energetic coincidence. The observed anisotropies disappear
drastically for temperatures above 1 K. We propose that our experimental
findings may be caused by the formation of a unidirectional stripe phase
oriented perpendicular to the in-plane field.Comment: 4 pages, 3 figure
A Fermi Fluid Description of the Half-Filled Landau Level
We present a many-body approach to calculate the ground state properties of a
system of electrons in a half-filled Landau level. Our starting point is a
simplified version of the recently proposed trial wave function where one
includes the antisymmetrization operator to the bosonic Laughlin state. Using
the classical plasma analogy, we calculate the pair-correlation function, the
static structure function and the ground state energy in the thermodynamic
limit. These results are in good agreement with the expected behavior at
.Comment: 4 pages, REVTEX, and 4 .ps file
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