43,140 research outputs found
Comment on ``Evidence for Anisotropic State of Two-Dimensional Electrons in High Landau Levels''
In a recent letter M. Lilly et al [PRL 82, 394 (1999)] have shown that a
highly anisotropic state can arise in certain two dimensional electron systems.
In the large square samples studied, resistances measured in the two
perpendicular directions are found to have a ratio that may be 60 or larger at
low temperature and at certain magnetic fields. In Hall bar measurements, the
anisotropy ratio is found to be much smaller (roughly 5). In this comment we
resolve this discrepancy by noting that the anisotropy of the underlying sheet
resistivities is correctly represented by Hall bar resistance measurements but
shows up exponentially enhanced in resistance measurements on square samples
due to simple geometric effects. We note, however, that the origin of this
underlying resistivity anisotropy remains unknown, and is not addressed here.Comment: 1 page, minor calculational error repaire
Magnetization-controlled spin transport in DyAs/GaAs layers
Electrical transport properties of DyAs epitaxial layers grown on GaAs have
been investigated at various temperatures and magnetic fields up to 12T. The
measured longitudinal resistances show two distinct peaks at fields around 0.2
and 2.5T which are believed to be related to the strong spin-disorder
scattering occurring at the phase transition boundaries induced by external
magnetic field. An empirical magnetic phase diagram is deduced from the
temperature dependent experiment, and the anisotropic transport properties are
also presented for various magnetic field directions with respect to the
current flow.Comment: 3 pages with 3 figure
Observation of a cyclotron harmonic spike in microwave-induced resistances in ultraclean GaAs/AlGaAs quantum wells
We report the observation of a colossal, narrow resistance peak that arises
in ultraclean (mobility 3X10^7cm^2/Vs) GaAs/AlGaAs quantum wells (QWs) under
millimeterwave irradiation and a weak magnetic field. Such a spike is
superposed on the 2nd harmonic microwave-induced resistance oscillations (MIRO)
but having an amplitude > 300% of the MIRO, and a typical FWHM ~50 mK,
comparable with the Landau level width. Systematic studies show a correlation
between the spike and a pronounced negative magnetoresistance in these QWs,
suggesting a mechanism based on the interplay of strong scatterers and smooth
disorder. Alternatively, the spike may be interpreted as a manifestation of
quantum interference between the quadrupole resonance and the higher-order
cyclotron transition in well-separated Landau levels.Comment: 4pages, 4figure
Crystallization in a model glass: influence of the boundary conditions
Using molecular dynamics calculations and the Voronoi tessellation, we study
the evolution of the local structure of a soft-sphere glass versus temperature
starting from the liquid phase at different quenching rates. This study is done
for different sizes and for two different boundary conditions namely the usual
cubic periodic boundary conditions and the isotropic hyperspherical boundary
conditions for which the particles evolve on the surface of a hypersphere in
four dimensions. Our results show that for small system sizes, crystallization
can indeed be induced by the cubic boundary conditions. On the other hand we
show that finite size effects are more pronounced on the hypersphere and that
crystallization is artificially inhibited even for large system sizes.Comment: 11 pages, 2 figure
TWITTER IN THE MARKETING
We report on a compact and highly efficient diode-end-pumped TEM00 Nd:YVO4 slab laser with an output power of 103 W and beam quality M2 1.5. The optical-to-optical efficiency was 41.5%. In electro-optically Q-switched operation. 83 W of average power at a pulse-repetition rate of 50 kHz with a pulse length of 11.3 ns was obtained. At a pulse-repetition rate of 10 kHz, 5.6 mJ of pulse energy, and 870 kW of peak power were measured
Reduction of -Regular Noncrossing Partitions
In this paper, we present a reduction algorithm which transforms -regular
partitions of to -regular partitions of .
We show that this algorithm preserves the noncrossing property. This yields a
simple explanation of an identity due to Simion-Ullman and Klazar in connection
with enumeration problems on noncrossing partitions and RNA secondary
structures. For ordinary noncrossing partitions, the reduction algorithm leads
to a representation of noncrossing partitions in terms of independent arcs and
loops, as well as an identity of Simion and Ullman which expresses the Narayana
numbers in terms of the Catalan numbers
Piezoelectric mechanism of orientation of stripe structures in two-dimensional electron systems
A piezoelectric mechanism of orientation of stripes in two-dimensional
quantum Hall systems in GaAs heterostructures is considered. The anisotropy of
the elastic moduli and the boundary of the sample are taken into account. It is
found that in the average the stripes line up with the [110] axis. In double
layer systems the wave vector of the stripe structure rotates from the [110] to
[100] axis if the period of density modulation becomes large than the
interlayer distance. From the experimental point of view it means that in
double layer systems anisotropic part of resistivity changes its sign under
variation of the external magnetic field.Comment: 8 page
Separation probabilities for products of permutations
We study the mixing properties of permutations obtained as a product of two
uniformly random permutations of fixed cycle types. For instance, we give an
exact formula for the probability that elements are in distinct
cycles of the random permutation of obtained as product of two
uniformly random -cycles
Semileptonic and nonleptonic decays in three--point QCD sum rules and factorization approach
We analyze the semileptonic transition with , in the framework of the three--point QCD sum rules and the nonleptonic
decay within the QCD factorization approach. We study to
and transition form factors by separating the mixture
of the and states. Using the transition form factors of
the , we analyze the nonleptonic decay. We also
present the decay amplitude and decay width of these decays in terms of the
transition form factors. The branching ratios of these channel modes are also
calculated at different values of the mixing angle and compared
with the existing experimental data for the nonleptonic case.Comment: 28 Pages, 20 Figures and 9 Table
Spatial oscillations in the spontaneous emission rate of an atom inside a metallic wedge
A method of images is applied to study the spontaneous emission of an atom
inside a metallic wedge with an opening angle of , where N is an
arbitrary positive integer. We show the method of images gives a rate formula
consistent with that from Quantum Electrodynamics. Using the method of images,
we show the correspondence between the oscillations in the spontaneous emission
rate and the closed-orbits of emitted photon going away and returning to the
atom inside the wedge. The closed-orbits can be readily constructed using the
method of images and they are also extracted from the spontaneous emission
rate.Comment: 8 figure
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