32 research outputs found
Absence of correlation between built-in electric dipole moment and quantum Stark effect in InAs/GaAs self-assembled quantum dots
We report significant deviations from the usual quadratic dependence of the
ground state interband transition energy on applied electric fields in
InAs/GaAs self-assembled quantum dots. In particular, we show that conventional
second-order perturbation theory fails to correctly describe the Stark shift
for electric field below kV/cm in high dots. Eight-band calculations demonstrate this effect is predominantly due to
the three-dimensional strain field distribution which for various dot shapes
and stoichiometric compositions drastically affects the hole ground state. Our
conclusions are supported by two independent experiments.Comment: 4 pages, 4 figure
A new species of planthopper belonging to the genus Oecleus Stål, 1862 (Hemiptera: Fulgoroidea: Cixiidae) from coconut palm (Cocos nucifera L) in Jamaica.
A new species of cixiid planthopper (Hemiptera: Fulgoroidea) in the genus Oecleus Stål, Oecleus mackaspringi sp. n., is described from Spring Garden, Jamaica. This new taxon is associated with coconut palm (Cocos nucifera L.) and was found while surveying palm plots with active cases of lethal yellowing (LY). This is the first report of the genus Oecleus from Jamaica. Sequence data for the COI gene and 18S gene are also provided
Navigation in Curved Space-Time
A covariant and invariant theory of navigation in curved space-time with
respect to electromagnetic beacons is written in terms of J. L. Synge's
two-point invariant world function. Explicit equations are given for navigation
in space-time in the vicinity of the Earth in Schwarzschild coordinates and in
rotating coordinates. The restricted problem of determining an observer's
coordinate time when their spatial position is known is also considered
Anomalous quantum confined Stark effects in stacked InAs/GaAs self-assembled quantum dots
Vertically stacked and coupled InAs/GaAs self-assembled quantum dots (SADs)
are predicted to exhibit a strong non-parabolic dependence of the interband
transition energy on the electric field, which is not encountered in single SAD
structures nor in other types of quantum structures. Our study based on an
eight-band strain-dependent Hamiltonian indicates that
this anomalous quantum confined Stark effect is caused by the three-dimensional
strain field distribution which influences drastically the hole states in the
stacked SAD structures.Comment: 4 pages, 4 figure
Fidelity of Quantum Interferometers
For a generic interferometer, the conditional probability density
distribution, , for the phase given measurement outcome ,
will generally have multiple peaks. Therefore, the phase sensitivity of an
interferometer cannot be adequately characterized by the standard deviation,
such as (the standard limit), or (the Heisenberg limit). We propose an alternative measure of phase
sensitivity--the fidelity of an interferometer--defined as the Shannon mutual
information between the phase shift \ and the measurement outcomes .
As an example application of interferometer fidelity, we consider a generic
optical Mach-Zehnder interferometer, used as a sensor of a classical field. We
find the surprising result that an entangled {\it N00N} state input leads to a
lower fidelity than a Fock state input, for the same photon number.Comment: 4 pages, 3 figure
A new species of planthopper in the genus Agoo Bahder & Bartlett (Hemiptera: Fulgoroidea: Derbidae) from coconut palm (Cocos nucifera L.) in Jamaica
A new species of the genus Agoo Bahder & Bartlett, Agoo beani sp. n. was found associated with coconut (Cocos nucifera L., Arecaceae) in Jamaica. This species was discovered as part of a survey of the Caribbean basin to document planthopper diversity on palms. Cytochrome c oxidase subunit I (COI) and 18S sequence data strongly support placement of the new species in Agoo. The morphological features of Omolicna cocoana Rodriguez-Leon & Hidalgo-Gato from Cuba are reviewed and this species transferred into the genus Agoo
Electronic structure of strained InP/GaInP quantum dots
We calculate the electronic structure of nm scale InP islands embedded in
. The calculations are done in the envelope approximation
and include the effects of strain, piezoelectric polarization, and mixing among
6 valence bands. The electrons are confined within the entire island, while the
holes are confined to strain induced pockets. One pocket forms a ring at the
bottom of the island near the substrate interface, while the other is above the
island in the GaInP. The two sets of hole states are decoupled. Polarization
dependent dipole matrix elements are calculated for both types of hole states.Comment: Typographical error corrected in strain Hamiltonia
Effects of Next-Nearest-Neighbor Repulsion on One-Dimensional Quarter-Filled Electron Systems
We examine effects of the next-nearest-neighbor repulsion on electronic
states of a one-dimensional interacting electron system which consists of
quarter-filled band and interactions of on-site and nearest-neighbor repulsion.
We derive the effective Hamiltonian for the electrons around wave number \pm
\kf (\kf: Fermi wave number) and apply the renormalization group method to
the bosonized Hamiltonian. It is shown that the next-nearest-neighbor repulsion
makes 4\kf-charge ordering unstable and suppresses the spin fluctuation.
Further the excitation gaps and spin susceptibility are also evaluated.Comment: 19 pages, 8 figures, submitted to J. Phys. Soc. Jp
Confinement of Interchain Hopping by Umklapp Scattering in Two-Coupled Chains
The effect of umklapp scattering on interchain hopping has been investigated
for two-coupled chains of interacting electrons with half-filled band. By
analyzing in terms of renormalization group method, we have found that
interchain hopping is renormalized to zero and is confined when a gap induced
by umklapp scattering becomes larger than a critical value. From a phase
diagram calculated on a plane of the interchain hopping and the gap, we discuss
a role of the correlation gap which has been studied in metallic state at
temperatures above spin density wave state in organic conductors.Comment: 5 pages, 3 figure
Linear Momentum Density in Quasistatic Electromagnetic Systems
We discuss a couple of simple quasistatic electromagnetic systems in which
the density of electromagnetic linear momentum can be easily computed. The
examples are also used to illustrate how the total electromagnetic linear
momentum, which may also be calculated by using the vector potential, can be
understood as a consequence of the violation of the action-reaction principle,
because a non-null external force is required to maintain constant the
mechanical linear momentum. We show how one can avoid the divergence in the
interaction linear electromagnetic momentum of a system composed by an
idealization often used in textbooks (an infinite straight current) and a point
charge.Comment: 22 pages, 5 figures, to appear in Eur. J. Phy