9,055 research outputs found
Pseudo diamagnetism of four component exciton condensates
We analyze the spin structure of the ground state of four-component exciton
condensates in coupled quantum wells as a function of spin-dependent
interactions and applied magnetic field. The four components correspond to the
degenerate exciton states characterized by and spin projections
to the axis of the structure. We show that in a wide range of parameters, the
chemical potential of the system increases as a function of magnetic field,
which manifests a pseudo-diamagnetism of the system. The transitions to
polarized two- and one-component condensates can be of the first-order in this
case. The predicted effects are caused by energy conserving mixing of
and excitons.Comment: 4 pages, 2 figure
Decohering d-dimensional quantum resistance
The Landauer scattering approach to 4-probe resistance is revisited for the
case of a d-dimensional disordered resistor in the presence of decoherence. Our
treatment is based on an invariant-embedding equation for the evolution of the
coherent reflection amplitude coefficient in the length of a 1-dimensional
disordered conductor, where decoherence is introduced at par with the disorder
through an outcoupling, or stochastic absorption, of the wave amplitude into
side (transverse) channels, and its subsequent incoherent re-injection into the
conductor. This is essentially in the spirit of B{\"u}ttiker's
reservoir-induced decoherence. The resulting evolution equation for the
probability density of the 4-probe resistance in the presence of decoherence is
then generalised from the 1-dimensional to the d-dimensional case following an
anisotropic Migdal-Kadanoff-type procedure and analysed. The anisotropy, namely
that the disorder evolves in one arbitrarily chosen direction only, is the main
approximation here that makes the analytical treatment possible. A
qualitatively new result is that arbitrarily small decoherence reduces the
localisation-delocalisation transition to a crossover making resistance moments
of all orders finite.Comment: 14 pages, 1 figure, revised version, to appear in Phys. Rev.
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
Fictitious Level Dynamics: A Novel Approach to Spectral Statistics in Disordered Conductors
We establish a new approach to calculating spectral statistics in disordered
conductors, by considering how energy levels move in response to changes in the
impurity potential. We use this fictitious dynamics to calculate the spectral
form factor in two ways. First, describing the dynamics using a Fokker-Planck
equation, we make a physically motivated decoupling, obtaining the spectral
correlations in terms of the quantum return probability. Second, from an
identity which we derive between two- and three-particle correlation functions,
we make a mathematically controlled decoupling to obtain the same result. We
also calculate weak localization corrections to this result, and show for two
dimensional systems (which are of most interest) that corrections vanish to
three-loop order.Comment: 35 pages in REVTeX format including 10 postscript figures; to be
published in a special issue (on Topics in Mesoscopic Physics) of the Journal
of Mathematical Physics, October 199
Bose-Einstein condensation of trapped polaritons in 2D electron-hole systems in a high magnetic field
The Bose-Einstein condensation (BEC) of magnetoexcitonic polaritons in
two-dimensional (2D) electron-hole system embedded in a semiconductor
microcavity in a high magnetic field is predicted. There are two physical
realizations of 2D electron-hole system under consideration: a graphene layer
and quantum well (QW). A 2D gas of magnetoexcitonic polaritons is considered in
a planar harmonic potential trap. Two possible physical realizations of this
trapping potential are assumed: inhomogeneous local stress or harmonic electric
field potential applied to excitons and a parabolic shape of the semiconductor
cavity causing the trapping of microcavity photons. The effective Hamiltonian
of the ideal gas of cavity polaritons in a QW and graphene in a high magnetic
field and the BEC temperature as functions of magnetic field are obtained. It
is shown that the effective polariton mass increases with
magnetic field as . The BEC critical temperature
decreases as and increases with the spring constant of the parabolic
trap. The Rabi splitting related to the creation of a magnetoexciton in a high
magnetic field in graphene and QW is obtained. It is shown that Rabi splitting
in graphene can be controlled by the external magnetic field since it is
proportional to , while in a QW the Rabi splitting does not depend on
the magnetic field when it is strong.Comment: 16 pages, 6 figures. accepted in Physical Review
Interindustry Wage Differentials in Australia, 1947-54
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91914/1/Kmenta-Inter-Industry_Wage.pd
Crossover from diffusive to strongly localized regime in two-dimensional systems
We have studied the conductance distribution function of two-dimensional
disordered noninteracting systems in the crossover regime between the diffusive
and the localized phases. The distribution is entirely determined by the mean
conductance, g, in agreement with the strong version of the single-parameter
scaling hypothesis. The distribution seems to change drastically at a critical
value very close to one. For conductances larger than this critical value, the
distribution is roughly Gaussian while for smaller values it resembles a
log-normal distribution. The two distributions match at the critical point with
an often appreciable change in behavior. This matching implies a jump in the
first derivative of the distribution which does not seem to disappear as system
size increases. We have also studied 1/g corrections to the skewness to
quantify the deviation of the distribution from a Gaussian function in the
diffusive regime.Comment: 4 pages, 4 figure
Magnetic field generation in Higgs inflation model
We study the generation of magnetic field in Higgs-inflation models where the
Standard Model Higgs boson has a large coupling to the Ricci scalar. We couple
the Higgs field to the Electromagnetic fields via a non- renormalizable
dimension six operator suppressed by the Planck scale in the Jordan frame. We
show that during Higgs inflation magnetic fields with present value
Gauss and comoving coherence length of can be generated in the
Einstein frame. The problem of large back-reaction which is generic in the
usual inflation models of magneto-genesis is avoided as the back-reaction is
suppressed by the large Higgs-curvature coupling.Comment: 10 pages, RevTeX
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.
The Zipf law for random texts with unequal probabilities of occurrence of letters and the Pascal pyramid
We model the generation of words with independent unequal probabilities of
occurrence of letters. We prove that the probability of occurrence of
words of rank has a power asymptotics. As distinct from the paper published
earlier by B. Conrad and M. Mitzenmacher, we give a brief proof by elementary
methods and obtain an explicit formula for the exponent of the power law.Comment: 4 page
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