85,468 research outputs found
Possible Reentrance of the Fractional Quantum Hall Effect in the Lowest Landau Level
In the framework of a recently developed model of interacting composite
fermions, we calculate the energy of different solid and Laughlin-type liquid
phases of spin-polarized composite fermions. The liquid phases have a lower
energy than the competing solids around the electronic filling factors
nu=4/11,6/17, and 4/19 and may thus be responsible for the fractional quantum
Hall effect at nu=4/11. The alternation between solid and liquid phases when
varying the magnetic field may lead to reentrance phenomena in analogy with the
observed reentrant integral quantum Hall effect.Comment: 4 pages, 3 figures; revised version accepted for publication in Phys.
Rev. Let
Quantum Phases in Partially Filled Landau Levels
We compare the energies of different electron solids, such as bubble crystals
with triangular and square symmetry and stripe phases, to those of correlated
quantum liquids in partially filled intermediate Landau levels. Multiple
transitions between these phases when varying the filling of the top-most
partially filled Landau level explain the observed reentrance of the integer
quantum Hall effect. The phase transitions are identified as first-order. This
leads to a variety of measurable phenomena such as the phase coexistence
between a Wigner crystal and a two-electron bubble phase in a Landau-level
filling-factor range , which has recently been observed in
transport measurements under micro-wave irradiation.Comment: 6 pages, 2 figures; to appear in "Proceedings of the 16th
International Conference on High Magnetic Fields in Semiconductor Physics
(SemiMag-16)
Local density of states of electron-crystal phases in graphene in the quantum Hall regime
We calculate, within a self-consistent Hartree-Fock approximation, the local
density of states for different electron crystals in graphene subject to a
strong magnetic field. We investigate both the Wigner crystal and bubble
crystals with M_e electrons per lattice site. The total density of states
consists of several pronounced peaks, the number of which in the negative
energy range coincides with the number of electrons M_e per lattice site, as
for the case of electron-solid phases in the conventional two-dimensional
electron gas. Analyzing the local density of states at the peak energies, we
find particular scaling properties of the density patterns if one fixes the
ratio nu_N/M_e between the filling factor nu_N of the last partially filled
Landau level and the number of electrons per bubble. Although the total density
profile depends explicitly on M_e, the local density of states of the lowest
peaks turns out to be identical regardless the number of electrons M_e. Whereas
these electron-solid phases are reminiscent to those expected in the
conventional two-dimensional electron gas in GaAs heterostructures in the
quantum Hall regime, the local density of states and the scaling relations we
highlight in this paper may be, in graphene, directly measured by spectroscopic
means, such as e.g. scanning tunneling microscopy.Comment: 8 pages, 7 figures; minor correction
Wage and Occupational Differences Between Black and White Men: Labor Market Discrimination in the Rural South
The existence of labor market discrimination based on race is well established.However, study continues into a variety of aspects of discrimination-among them the extent to which it exists in different regions. Gwartney has estimated the ratio of black to white earnings to be between .83 and .88 for the North and between .68 and .74 for the South. Masters, in a study of earnings differentials between black and white men, found a ratio of .79 for the non-South and .69 for the South. Although considerable literature has developed concerning earnings differentials, wage discrimination in rural areas is one topic which has received relatively little attention. In an attempt to eliminate this oversight this paper concentrates on the extent of wage differences between black and white men in the rural South attributable to labor market discrimination
On the self-similarity in quantum Hall systems
The Hall-resistance curve of a two-dimensional electron system in the
presence of a strong perpendicular magnetic field is an example of
self-similarity. It reveals plateaus at low temperatures and has a fractal
structure. We show that this fractal structure emerges naturally in the
Hamiltonian formulation of composite fermions. After a set of transformations
on the electronic model, we show that the model, which describes interacting
composite fermions in a partially filled energy level, is self-similar. This
mathematical property allows for the construction of a basis of higher
generations of composite fermions. The collective-excitation dispersion of the
recently observed 4/11 fractional-quantum-Hall state is discussed within the
present formalism.Comment: 7 pages, 4 figures; version accepted for publication in Europhys.
Lett., new version contains energy calculations for collective excitations of
the 4/11 stat
Structural lubricity: Role of dimension and symmetry
When two chemically passivated solids are brought into contact, interfacial
interactions between the solids compete with intrabulk elastic forces. The
relative importance of these interactions, which are length-scale dependent,
will be estimated using scaling arguments. If elastic interactions dominate on
all length scales, solids will move as essentially rigid objects. This would
imply superlow kinetic friction in UHV, provided wear was absent. The results
of the scaling study depend on the symmetry of the surfaces and the
dimensionalities of interface and solids. Some examples are discussed
explicitly such as contacts between disordered three-dimensional solids and
linear bearings realized from multiwall carbon nanotubes.Comment: 7 pages, 1 figur
Clickers R Us: A Technology Approach for Assessing Online Learning in the Classroom for Blended Learning Courses
Blended learning integrates online delivery of materials through web pages, discussion boards, and/or e-mail with traditional teaching methods including lectures, guided discussions, seminars, or tutorials. In blended learning, specific course material is outsourced to textbook or online learning. When students are brought back to the classroom to apply what they learned online, the instructor\u27s immediate goals are to: (a) assess the individual gains of online learning, (b) review critical material, and (c) provide formative feedback. The paper explains how a classroom response system can provide an interactive classroom environment to accomplish these goals quickly and interactively. The authors present data from two courses where classroom response systems were effectively used for assessment, review, and feedback
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