22,675 research outputs found
The Intrinsic Spin Hall Conductivity in a Generalized Rashba Model
We calculate the intrinsic spin Hall conductivity \sigma^{\mathrm{sH}} of a
two-dimensional electron system within a generalized Rashba model, showing that
it is, in general, finite and model-dependent. Considering arbitrary band
dispersion, we find that \sigma^{\mathrm{sH}} in the presence of the
linear-in-momentum spin-orbit coupling of the Rashba form does not vanish in
the presence of impurities except for the precisely parabolic spectrum. We
show, using the linear response Kubo formalism, how the exact cancellation
happens for the quadratic dispersion, and why it does not occur in general. We
derive a simple quasiclassical formula for \sigma^{\mathrm{sH}} in terms of the
Fermi momenta for the two electron chiralities, and find that
\sigma^{\mathrm{sH}} is in general of the order of the squared strength of the
Rashba term
Factorization of finite temperature graphs in thermal QED
We extend our previous analysis of gauge and Dirac fields in the presence of
a chemical potential. We consider an alternate thermal operator which relates
in a simple way the Feynman graphs in QED at finite temperature and charge
density to those at zero temperature but non-zero chemical potential. Several
interesting features of such a factorization are discussed in the context of
the thermal photon and fermion self-energies.Comment: 4 page
Hyperspherical partial wave theory applied to electron hydrogen-atom ionization calculation for equal energy sharing kinematics
Hyperspherical partial wave theory has been applied here in a new way in the
calculation of the triple differential cross sections for the ionization of
hydrogen atoms by electron impact at low energies for various
equal-energy-sharing kinematic conditions. The agreement of the cross section
results with the recent absolute measurements of R\"oder \textit {et al} [51]
and with the latest theoretical results of the ECS and CCC calculations [29]
for different kinematic conditions at 17.6 eV is very encouraging. The other
calculated results, for relatively higher energies, are also generally
satisfactory, particularly for large geometries. In view of the
present results, together with the fact that it is capable of describing
unequal-energy-sharing kinematics [35], it may be said that the hyperspherical
partial wave theory is quite appropriate for the description of ionization
events of electron-hydrogen type systems. It is also clear that the present
approach in the implementation of the hyperspherical partial wave theory is
very appropriate.Comment: 16 pages, 9 figures, LaTeX file and EPS figures. To appear in Phys.
Rev.
Thermal Operator and Cutting Rules at Finite Temperature and Chemical Potential
In the context of scalar field theories, both real and complex, we derive the
cutting description at finite temperature (with zero/finite chemical potential)
from the cutting rules at zero temperature through the action of a simple
thermal operator. We give an alternative algebraic proof of the largest time
equation which brings out the underlying physics of such a relation. As an
application of the cutting description, we calculate the imaginary part of the
one loop retarded self-energy at zero/finite temperature and finite chemical
potential and show how this description can be used to calculate the dispersion
relation as well as the full physical self-energy of thermal particles.Comment: 17 pages, 13 figures. Added references, version to appear in Physical
Review
Griffiths phase in diluted magnetic semiconductors
We study the effects of disorder in the vicinity of the ferromagnetic
transition in a diluted magnetic semiconductor in the strongly localized
regime. We derive an effective polaron Hamiltonian, which leads to the
Griffiths phase above the ferromagnetic transition point. The Griffiths-McCoy
effects yield non-perturbative contributions to the dynamic susceptibility. We
explicitly derive the long-time susceptibility, which has a pseudo-scaling
form, with the dynamic critical exponent being expressed through the
percolation indices.Comment: 4 pages, final version as publishe
Thermal Effective Lagrangian of Static Gravitational Fields
We compute the effective Lagrangian of static gravitational fields
interacting with thermal fields. Our approach employs the usual imaginary time
formalism as well as the equivalence between the static and space-time
independent external gravitational fields. This allows to obtain a closed form
expression for the thermal effective Lagrangian in space-time dimensions.Comment: Accepted for publication in the Physical Review
Entropic corrections to Newton's law
In this short letter we calculate separately the generalized uncertainty
principle (GUP) and self gravitational corrections to the Newton's
gravitational formula. We show that for a complete description of the GUP and
self-gravity effects, both temperature and the entropy must be modified.Comment: 4 pages, Accepted for publication in "Physica Scripta",Title changed,
Major revisio
Wave Functions and Energies of Magnetopolarons in Semiconductor Quantum Wells
The classification of magnetopolarons in semiconductor quantum wells (QW) is
represented. Magnetopolarons appear due to the Johnson - Larsen effect. The
wave functions of usual and combined magnetopolarons are obtained by the
diodanalization of the Schrodinger equation.Comment: 7 pages, 2 figure
Development of an Advanced Force Field for Water using Variational Energy Decomposition Analysis
Given the piecewise approach to modeling intermolecular interactions for
force fields, they can be difficult to parameterize since they are fit to data
like total energies that only indirectly connect to their separable functional
forms. Furthermore, by neglecting certain types of molecular interactions such
as charge penetration and charge transfer, most classical force fields must
rely on, but do not always demonstrate, how cancellation of errors occurs among
the remaining molecular interactions accounted for such as exchange repulsion,
electrostatics, and polarization. In this work we present the first generation
of the (many-body) MB-UCB force field that explicitly accounts for the
decomposed molecular interactions commensurate with a variational energy
decomposition analysis, including charge transfer, with force field design
choices that reduce the computational expense of the MB-UCB potential while
remaining accurate. We optimize parameters using only single water molecule and
water cluster data up through pentamers, with no fitting to condensed phase
data, and we demonstrate that high accuracy is maintained when the force field
is subsequently validated against conformational energies of larger water
cluster data sets, radial distribution functions of the liquid phase, and the
temperature dependence of thermodynamic and transport water properties. We
conclude that MB-UCB is comparable in performance to MB-Pol, but is less
expensive and more transferable by eliminating the need to represent
short-ranged interactions through large parameter fits to high order
polynomials
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