8,239 research outputs found
Dynamic equation for quantum Hall bilayers with spontaneous interlayer coherence: The low-density limit
The bilayer systems exhibit the Bose-Einstein condensation of excitons that
emerge due to Coulomb pairing of electrons belonging to one layer with the
holes belonging to the other layer. Here we present the microscopic derivation
of the dynamic equation for the condensate wave function at a low density of
electron-hole () pairs in a strong magnetic field perpendicular to the
layers and an electric field directed along the layers. From this equation we
obtain the dispersion law for collective excitations of the condensate and
calculate the electric charge of the vortex in the exciton condensate. The
critical interlayer spacing, the excess of which leads to a collapse of the
superfluid state, is estimated. In bilayer systems with curved conducting
layers, the effective mass of the pair becomes the function of the
pair coordinates, the regions arise, where the energy of the pair is
lowered (exciton traps), and lastly pairs can gain the polarization in
the basal plane. This polarization leads to the appearance of quantized
vortices even at zero temperature.Comment: 8 page
Boundedness of Pseudodifferential Operators on Banach Function Spaces
We show that if the Hardy-Littlewood maximal operator is bounded on a
separable Banach function space and on its associate space
, then a pseudodifferential operator
is bounded on whenever the symbol belongs to the
H\"ormander class with ,
or to the the Miyachi class
with ,
. This result is applied to the case of
variable Lebesgue spaces .Comment: To appear in a special volume of Operator Theory: Advances and
Applications dedicated to Ant\'onio Ferreira dos Santo
Mesoscopic conductance fluctuations in dirty quantum dots with single channel leads
We consider a distribution of conductance fluctuations in quantum dots with
single channel leads and continuous level spectra and we demonstrate that it
has a distinctly non-Gaussian shape and strong dependence on time-reversal
symmetry, in contrast to an almost Gaussian distribution of conductances in a
disordered metallic sample connected to a reservoir by broad multi-channel
leads. In the absence of time-reversal symmetry, our results obtained within
the diagrammatic approach coincide with those derived within non-perturbative
techniques. In addition, we show that the distribution has lognormal tails for
weak disorder, similar to the case of broad leads, and that it becomes almost
lognormal as the amount of disorder is increased towards the Anderson
transition.Comment: 14 pages in the ReVTeX preprint format, including 5 postscript
figures; to be published in J.Phys.:Cond.Mat., 199
Ejection Energy of Photoelectrons in Strong Field Ionization
We show that zero ejection energy of the photoelectrons is classically
impossible for hydrogen-like ions, even when field ionization occurs
adiabatically. To prove this we transform the basic equations to those
describing two 2D anharmonic oscillators. The same method yields an alternative
way to derive the anomalous critical field of hydrogen-like ions. The
analytical results are confirmed and illustrated by numerical simulations. PACS
Number: 32.80.RmComment: 7 pages, REVTeX, postscript file including the figures is available
at http://www.physik.th-darmstadt.de/tqe/dieter/publist.html or via anonymous
ftp from ftp://tqe.iap.physik.th-darmstadt.de/pub/dieter/publ_I_pra_pre.ps,
accepted for publication in Phys. Rev.
Optics with Quantum Hall Skyrmions
A novel type of charged excitation, known as a Skyrmion, has recently been
discovered in quantum Hall systems with filling factor near \nu = 1. A Skyrmion
-- which can be thought of as a topological twist in the spin density of the
electron gas -- has the same charge as an electron, but a much larger spin. In
this review we present a detailed theoretical investigation of the optical
properties of Skyrmions. Our results provide means for the optical detection of
Skyrmions using photoluminescence (PL) spectroscopy. We first consider the
optical properties of Skyrmions in disordered systems. A calculation of the
luminescence energy reveals a special optical signature which allows us to
distinguish between Skyrmions and ordinary electrons. Two experiments to
measure the optical signature are proposed. We then turn to the optical
properties of Skyrmions in pure systems. We show that, just like an ordinary
electron, a Skyrmion may bind with a hole to form a Skyrmionic exciton. The
Skyrmionic exciton can have a lower energy than the ordinary magnetoexciton.
The optical signature of Skyrmions is found to be a robust feature of the PL
spectrum in both disordered and pure systems.Comment: 31 pages, LaTex, 11 eps figures. ijmpb style file included. Review
article submitted to Int. J. Mod. Phys.
Cosine and Sine Operators Related with Orthogonal Polynomial Sets on the Intervall [-1,1]
The quantization of phase is still an open problem. In the approach of
Susskind and Glogower so called cosine and sine operators play a fundamental
role. Their eigenstates in the Fock representation are related with the
Chebyshev polynomials of the second kind. Here we introduce more general cosine
and sine operators whose eigenfunctions in the Fock basis are related in a
similar way with arbitrary orthogonal polynomial sets on the intervall [-1,1].
To each polynomial set defined in terms of a weight function there corresponds
a pair of cosine and sine operators. Depending on the symmetry of the weight
function we distinguish generalized or extended operators. Their eigenstates
are used to define cosine and sine representations and probability
distributions. We consider also the inverse arccosine and arcsine operators and
use their eigenstates to define cosine-phase and sine-phase distributions,
respectively. Specific, numerical and graphical results are given for the
classical orthogonal polynomials and for particular Fock and coherent states.Comment: 1 tex-file (24 pages), 11 figure
Quantum transport thermometry for electrons in graphene
We propose a method of measuring the electron temperature in mesoscopic
conductors and demonstrate experimentally its applicability to micron-size
graphene devices in the linear-response regime (, the bath
temperature). The method can be {especially useful} in case of overheating,
. It is based on analysis of the correlation function of mesoscopic
conductance fluctuations. Although the fluctuation amplitude strongly depends
on the details of electron scattering in graphene, we show that extracted
from the correlation function is insensitive to these details.Comment: 4 pages, 4 figures; final version, as publishe
Two-dimensional magnetoexcitons in the presence of spin-orbit coupling
We study theoretically the effect of spin-orbit coupling on quantum well
excitons in a strong magnetic field. We show that, in the presence of an
in-plane field component, the excitonic absorption spectrum develops a
double-peak structure due to hybridization of bright and dark magnetoexcitons.
If the Rashba and Dresselhaus spin-orbit constants are comparable, the
magnitude of splitting can be tuned in a wide interval by varying the azimuthal
angle of the in-plane field. We also show that the interplay between spin-orbit
and Coulomb interactions leads to an anisotropy of exciton energy dispersion in
the momentum plane. The results suggest a way for direct optical measurements
of spin-orbit parameters.Comment: 9 pages, 6 figure
Molecular Phylogenetics of Diurnal Birds of Prey in the Avian Accipitridae Family.
The avian family Accipitridae includes 240 species and 60 genera of hawks, eagles, Old World vultures, kites, accipiters, goshawks and harriers. Phylogeny for Accipitridae has been difficult to resolve with morphological data such that non-monophyly of subfamilies and genera was suspected. This study used mitochondrial and nuclear sequence data to resolve the phylogeny for Accipitridae taxa. Extensive sampling of nominal species and genera (75% of all species and 97% of genera) identified non-monophyly for most genera and subfamilies/subgroups and some species.
Monophyly of sea eagles (Haliaeetinae), booted eagles (Aquilinae), Aegypinae Old World Vultures, goshawks (Melieraxinae) and harriers (Circinae) was supported; however, none of the kite subfamilies (Milvinae, Perninae and Elaninae), Accipiters (Accipitrinae), harpy eagles (Harpiinae) and snake eagles (Circaetinae) formed monophyletic groups. Specialized limb morphology relating to predation on cavity-nesting species shared by the gymnogene (Polyboroides typus) and the Crane Hawk (Geranospiza caerulescens) is an example of convergent evolution as the two species were not closely related.
The nominal genera Buteo, Buteogallus, Accipiter, Circaetus, Hieraaetus, Spizaetus, Aquila, Haliaeetus and Leucopternis were not monophyletic. Investigations at or within the level of species revealed non-monophyly for Hieraaetus fasciatus and H. morphnoides, supporting recognition of H. spilogaster and H. weiskeii as distinct species. Complicated and non-monophyletic relationships among the subspecies of Leucopternis albicollis and L. occidentalis require further investigation to resolve taxonomic nomenclature. Such extensive non-phylogenetic taxonomy at multiple levels emphasizes the need for major taxonomic revision within the Accipitridae.
Investigations of genetic diversity and population structure within the harpy eagle (Harpia harpyja) found moderate to high levels of genetic diversity with 417 bases of the mitochondrial control region from 66 harpy eagles. There was no evidence of complete barriers to historical gene flow, however significant genetic differentiation between harpy eagles from Central America and South America was found. Estimates of gene flow were asymmetric with the vast majority of migration in the direction from Central America into South America, suggesting that habitat reduction and fragmentation in Central America may have forced southern migration. Conservation strategies for harpy eagles should aim to maintain gene flow between southern Central America and northern South America.Ph.D.Ecology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/57684/2/hlerner_1.pd
Concentration dependence of the transition temperature in metallic spin glasses
The dependence of the transition temperature in terms of the
concentration of magnetic impurities in spin glasses is explained on the
basis of a screened RKKY interaction. The two observed power laws, at
low and for intermediate , are described in a unified
approach.Comment: 4 page
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