23,337 research outputs found
Approximation for discrete Fourier transform and application in study of three-dimensional interacting electron gas
The discrete Fourier transform is approximated by summing over part of the
terms with corresponding weights. The approximation reduces significantly the
requirement for computer memory storage and enhances the numerical computation
efficiency with several orders without loosing accuracy. As an example, we
apply the algorithm to study the three-dimensional interacting electron gas
under the renormalized-ring-diagram approximation where the Green's function
needs to be self-consistently solved. We present the results for the chemical
potential, compressibility, free energy, entropy, and specific heat of the
system. The ground-state energy obtained by the present calculation is compared
with the existing results of Monte Carlo simulation and random-phase
approximation.Comment: 11 pages, 13 figure
Berry phase effect in anomalous thermoelectric transport
We develop a theory of Berry phase effect in anomalous transport in
ferromagnets driven by statistical forces such as the gradient of temperature
or chemical potential. Here a charge Hall current arises from the Berry phase
correction to the orbital magnetization rather than from the anomalous velocity
which does not exist in the absence of a mechanical force. A finite-temperature
formula for the orbital magnetization is derived, which enables us to provide
an explicit expression for the off-diagonal thermoelectric conductivity, to
establish the Mott relation between the anomalous Nernst and Hall effects, and
to reaffirm the Onsager relations between reciprocal thermoelectric
conductivities. A first-principles evaluation of our expression is carried out
for the material CuCrSeBr, obtaining quantitative agreement
with a recent experiment.Comment: Published version in PR
Suppression of dephasing by qubit motion in superconducting circuits
We suggest and demonstrate a protocol which suppresses dephasing due to the
low-frequency noise by qubit motion, i.e., transfer of the logical qubit of
information in a system of physical qubits. The protocol requires
only the nearest-neighbor coupling and is applicable to different qubit
structures. We further analyze its effectiveness against noises with arbitrary
correlations. Our analysis, together with experiments using up to three
superconducting qubits, shows that for the realistic uncorrelated noises, qubit
motion increases the dephasing time of the logical qubit as . In
general, the protocol provides a diagnostic tool to measure the noise
correlations.Comment: 5 pages with 3 embedded figures, plus supplementary informatio
Electric Transport Theory of Dirac Fermions in Graphene
Using the self-consistent Born approximation to the Dirac fermions under
finite-range impurity scatterings, we show that the current-current correlation
function is determined by four-coupled integral equations. This is very
different from the case for impurities with short-range potentials. As a test
of the present approach, we calculate the electric conductivity in graphene for
charged impurities with screened Coulomb potentials. The obtained conductivity
at zero temperature varies linearly with the carrier concentration, and the
minimum conductivity at zero doping is larger than the existing theoretical
predictions, but still smaller than that of the experimental measurement. The
overall behavior of the conductivity obtained by the present calculation at
room temperature is similar to that at zero temperature except the minimum
conductivity is slightly larger.Comment: 6 pages, 3 figure
Effect of quantum fluctuations on structural phase transitions in SrTiO_3 and BaTiO_3
Using path-integral Monte Carol simulations and an ab initio effective
Hamiltonian, we study the effects of quantum fluctuations on structural phase
transitions in the cubic perovskite compounds SrTiO3 and BaTiO3. We find
quantum fluctuations affect ferroelectric (FE) transitions more strongly than
antiferrodistortive (AFD) ones, even though the effective mass of a single FE
local mode is larger. For SrTiO3 we find that the quantum fluctuations suppress
the FE transition completely, and reduce the AFD transition temperature from
130K to 110K. For BaTiO3, quantum fluctuations do not affect the order of the
transition, but do reduce the transition temperature by 35-50 K. The
implications of the calculations are discussed.Comment: Revtex (preprint style, 14 pages) + 2 postscript figures. A version
in two-column article style with embedded figures is available at
http://electron.rutgers.edu/~dhv/preprints/index.html#wz_qs
The properties of kaonic nuclei in relativistic mean-field theory
The static properties of some possible light and moderate kaonic nuclei, from
C to Ti, are studied in the relativistic mean-field theory. The 1s and 1p state
binding energies of are in the range of MeV and
MeV, respectively. The binding energies of 1p states increase monotonically
with the nucleon number A. The upper limit of the widths are about
MeV for the 1s states, and about MeV for the 1p states. The lower
limit of the widths are about MeV for the 1s states, and
MeV for the 1p states. If MeV, the discrete bound states
should be identified in experiment. The shrinkage effect is found in the
possible kaonic nuclei. The interior nuclear density increases obviously, the
densest center density is about .Comment: 9 pages, 2 tables and 1 figure, widths are considered, changes a lo
Magnetoresistance due to Domain Walls in Micron Scale Fe Wires with Stripe Domains
The magnetoresistance (MR) associated with domain boundaries has been
investigated in microfabricated bcc Fe (0.65 to 20 m linewidth) wires with
controlled stripe domains. Domain configurations have been characterized using
magnetic force microscopy. MR measurements as a function of field angle,
temperature and domain configuration are used to estimate MR contributions due
to resistivity anisotropy and domain walls. Evidence is presented that domain
boundaries enhance the conductivity in such microstructures over a broad range
of temperatures (1.5 K to 80 K).Comment: 8 pages, 3 postscript figures, and 2 jpg images (Fig 1 and 2) to
appear in IEEE Transactions on Magnetics (Fall 1998
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