8,597 research outputs found
Heitler-London model for acceptor-acceptor interactions in doped semiconductors
The interactions between acceptors in semiconductors are often treated in
qualitatively the same manner as those between donors. Acceptor wave functions
are taken to be approximately hydrogenic and the standard hydrogen molecule
Heitler-London model is used to describe acceptor-acceptor interactions. But
due to valence band degeneracy and spin-orbit coupling, acceptor states can be
far more complex than those of hydrogen atoms, which brings into question the
validity of this approximation. To address this issue, we develop an
acceptor-acceptor Heitler-London model using single-acceptor wave functions of
the form proposed by Baldereschi and Lipari, which more accurately capture the
physics of the acceptor states. We calculate the resulting acceptor-pair energy
levels and find, in contrast to the two-level singlet-triplet splitting of the
hydrogen molecule, a rich ten-level energy spectrum. Our results, computed as a
function of inter-acceptor distance and spin-orbit coupling strength, suggest
that acceptor-acceptor interactions can be qualitatively different from
donor-donor interactions, and should therefore be relevant to the control of
two-qubit interactions in acceptor-based qubit implementations, as well as the
magnetic properties of a variety of p-doped semiconductor systems. Further
insight is drawn by fitting numerical results to closed-form energy-level
expressions obtained via an acceptor-acceptor Hubbard model.Comment: 19 pages, 10 figures, text revised, figure quality improved,
additional references adde
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A Pilot Study to Evaluate an Integrated Phonics and Language Programme for the Teaching of Reading to Deaf and Hearing Children
Photomechanical Investigation of Structural Behavior of Gyroscope Components. Task IV - Analysis of Initial Redesign of AB5-K8 GYROSCOPE
Photomechanics of structure and materials in redesigned AB5-K8 gyroscope component
Gallium(III)-Promoted Halocyclizations of 1,6-Diynes
Adrian Landreth was an REU student, summer 2014Cyclization of 1,6-diynes promoted by stoichiometric Ga(III) halides produces vinyl halides in good to excellent yields. Under acidic conditions, initially formed iodocyclization products undergo in situ Friedel-Crafts cyclizations, giving access to iodo-indenopyridines. The application of the vinyl halides in cross-coupling reactions has been explored, and mechanistic aspects of the cyclization are discussed.HIGMS CMLD Initiative (P50 GM067041)
NSF REU - Adrian Landreth support (CHE 1156666)
NSF - NMR purchase (CHE 0619339)
NSF - HRMS purchase (CHE0443618
Quantum Calculation of Inelastic CO Collisions with H. II. Pure Rotational Quenching of High Rotational Levels
Carbon monoxide is a simple molecule present in many astrophysical
environments, and collisional excitation rate coefficients due to the dominant
collision partners are necessary to accurately predict spectral line
intensities and extract astrophysical parameters. We report new quantum
scattering calculations for rotational deexcitation transitions of CO induced
by H using the three-dimensional potential energy surface~(PES) of Song et al.
(2015). State-to-state cross sections for collision energies from 10 to
15,000~cm and rate coefficients for temperatures ranging from 1 to
3000~K are obtained for CO(, ) deexcitation from to all lower
levels, where is the rotational quantum number. Close-coupling and
coupled-states calculations were performed in full-dimension for =1-5, 10,
15, 20, 25, 30, 35, 40, and 45 while scaling approaches were used to estimate
rate coefficients for all other intermediate rotational states. The current
rate coefficients are compared with previous scattering results using earlier
PESs. Astrophysical applications of the current results are briefly discussed.Comment: 8 figures, 1 tabl
Modelling gravity on a hyper-cubic lattice
We present an elegant and simple dynamical model of symmetric, non-degenerate
(n x n) matrices of fixed signature defined on a n-dimensional hyper-cubic
lattice with nearest-neighbor interactions. We show how this model is related
to General Relativity, and discuss multiple ways in which it can be useful for
studying gravity, both classical and quantum. In particular, we show that the
dynamics of the model when all matrices are close to the identity corresponds
exactly to a finite-difference discretization of weak-field gravity in harmonic
gauge. We also show that the action which defines the full dynamics of the
model corresponds to the Einstein-Hilbert action to leading order in the
lattice spacing, and use this observation to define a lattice analogue of the
Ricci scalar and Einstein tensor. Finally, we perform a mean-field analysis of
the statistical mechanics of this model.Comment: 5 page
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