2,401 research outputs found
An analysis of the fluctuation potential in the modified Poisson-Boltzmann theory for restricted primitive model electrolytes
An approximate analytical solution to the fluctuation potential problem in
the modified Poisson-Boltzmann theory of electrolyte solutions in the
restricted primitive model is presented. The solution is valid for all
inter-ionic distances, including contact values. The fluctuation potential
solution is implemented in the theory to describe the structure of the
electrolyte in terms of the radial distribution functions, and to calculate
some aspects of thermodynamics, viz., configurational reduced energies, and
osmotic coefficients. The calculations have been made for symmetric valence 1:1
systems at the physical parameters of ionic diameter m,
relative permittivity 78.5, absolute temperature 298 K, and molar
concentrations 0.1038, 0.425, 1.00, and 1.968. Radial distribution functions
are compared with the corresponding results from the symmetric
Poisson-Boltzmann, and the conventional and modified Poisson-Boltzmann
theories. Comparisons have also been done for the contact values of the radial
distributions, reduced configurational energies, and osmotic coefficients as
functions of electrolyte concentration. Some Monte Carlo simulation data from
the literature are also included in the assessment of the thermodynamic
predictions. Results show a very good agreement with the Monte Carlo results
and some improvement for osmotic coefficients and radial distribution functions
contact values relative to these theories. The reduced energy curve shows
excellent agreement with Monte Carlo data for molarities up to 1 mol/dm.Comment: 16 pages, 8 figures, 3 table
Anisotropic electron g-factor in quantum dots with spin-orbit interaction
g-factor tuning of electrons in quantum dots is studied as function of
in-plane and perpendicular magnetic fields for different confinements. Rashba
and Dresselhaus effects are considered, and comparison is made between wide-
and narrow-gap materials. The interplay between magnetic fields and intrinsic
spin-orbit coupling is analyzed, with two distinct phases found in the spectrum
for GaAs in perpendicular field. The anisotropy of the g-factor is reported,
and good agreement with available experimental findings is obtained.Comment: 5 pages, 4 figs. (higher resol. figs. under request
Kondo screening suppression by spin-orbit interaction in quantum dots
We study the transport properties of a quantum dot embedded in an
Aharonov-Bohm ring in the presence of spin-orbit interactions. Using a
numerical renormalization group analysis of the system in the Kondo regime, we
find that the competition of Aharonov-Bohm and spin-orbit dynamical phases
induces a strong suppression of the Kondo state singlet, somewhat akin to an
effective intrinsic magnetic field in the system. This effective field breaks
the spin degeneracy of the localized state and produces a finite magnetic
moment in the dot. By introducing an {\em in-plane} Zeeman field we show that
the Kondo resonance can be fully restored, reestablishing the spin singlet and
a desired spin filtering behavior in the Kondo regime, which may result in full
spin polarization of the current through the ring.Comment: 4 pages, 4 figure
Charge qubits and limitations of electrostatic quantum gates
We investigate the characteristics of purely electrostatic interactions with
external gates in constructing full single qubit manipulations. The quantum bit
is naturally encoded in the spatial wave function of the electron system.
Single-electron{transistor arrays based on quantum dots or insulating
interfaces typically allow for electrostatic controls where the inter-island
tunneling is considered constant, e.g. determined by the thickness of an
insulating layer. A representative array of 3x3 quantum dots with two mobile
electrons is analyzed using a Hubbard Hamiltonian and a capacitance matrix
formalism. Our study shows that it is easy to realize the first quantum gate
for single qubit operations, but that a second quantum gate only comes at the
cost of compromising the low-energy two-level system needed to encode the
qubit. We use perturbative arguments and the Feshbach formalism to show that
the compromising of the two-level system is a rather general feature for
electrostatically interacting qubits and is not just related to the specific
details of the system chosen. We show further that full implementation requires
tunable tunneling or external magnetic fields.Comment: 7 pages, 5 figures, submitted to PR
Impurity-enhanced Aharonov-Bohm effect in neutral quantum-ring magnetoexcitons
We study the role of impurity scattering on the photoluminescence (PL)
emission of polarized magnetoexcitons. We consider systems where both the
electron and hole are confined on a ring structure (quantum rings) as well as
on a type-II quantum dot. Despite their neutral character, excitons exhibit
strong modulation of energy and oscillator strength in the presence of magnetic
fields. Scattering impurities enhance the PL intensity on otherwise "dark"
magnetic field windows and non-zero PL emission appears for a wide magnetic
field range even at zero temperature. For higher temperatures, impurity-induced
anticrossings on the excitonic spectrum lead to unexpected peaks and valleys on
the PL intensity as function of magnetic field. Such behavior is absent on
ideal systems and can account for prominent features in recent experimental
results.Comment: 7 pages, 7 figures, RevTe
Spatial correlations in chaotic nanoscale systems with spin-orbit coupling
We investigate the statistical properties of wave functions in chaotic
nanostructures with spin-orbit coupling (SOC), focussing in particular on
spatial correlations of eigenfunctions. Numerical results from a microscopic
model are compared with results from random matrix theory in the crossover from
the gaussian orthogonal to the gaussian symplectic ensembles (with increasing
SOC); one- and two-point distribution functions were computed to understand the
properties of eigenfunctions in this crossover. It is found that correlations
of wave function amplitudes are suppressed with SOC; nevertheless,
eigenfunction correlations play a more important role in the two-point
distribution function(s), compared to the case with vanishing SOC. Experimental
consequences of our results are discussed.Comment: Submitted to PR
Zero-field Kondo splitting and quantum-critical transition in double quantum dots
Double quantum dots offer unique possibilities for the study of many-body
correlations. A system containing one Kondo dot and one effectively
noninteracting dot maps onto a single-impurity Anderson model with a structured
(nonconstant) density of states. Numerical renormalization-group calculations
show that while band filtering through the resonant dot splits the Kondo
resonance, the singlet ground state is robust. The system can also be
continuously tuned to create a pseudogapped density of states and access a
quantum critical point separating Kondo and non-Kondo phases.Comment: 4 pages, 4 figures; Accepted for publication in Physical Review
Letter
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