29,541 research outputs found
Pairing and density-wave phases in Boson-Fermion mixtures at fixed filling
We study a mixture of fermionic and bosonic cold atoms on a two-dimensional
optical lattice, where the fermions are prepared in two hyperfine (isospin)
states and the bosons have Bose-Einstein condensed (BEC). The coupling between
the fermionic atoms and the bosonic fluctuations of the BEC has similarities
with the electron-phonon coupling in crystals. We study the phase diagram for
this system at fixed fermion density of one per site (half-filling). We find
that tuning of the lattice parameters and interaction strengths (for
fermion-fermion, fermion-boson and boson-boson interactions) drives the system
to undergo antiferromagnetic ordering, s-wave and d-wave pairing
superconductivity or a charge density wave phase. We use functional
renormalization group analysis where retardation effects are fully taken into
account by keeping the frequency dependence of the interaction vertices and
self-energies. We calculate response functions and also provide estimates of
the energy gap associated with the dominant order, and how it depends on
different parameters of the problem.Comment: 5 pages, 3 figure
Analyses of composite structures
Stiffness and strength analyses on composite cross-ply and helical wound cylinders and flat laminate structure
Renormalization-group approach to superconductivity: from weak to strong electron-phonon coupling
We present the numerical solution of the renormalization group (RG) equations
derived in Ref. [1], for the problem of superconductivity in the presence of
both electron-electron and electron-phonon coupling at zero temperature. We
study the instability of a Fermi liquid to a superconductor and the RG flow of
the couplings in presence of retardation effects and the crossover from weak to
strong coupling. We show that our numerical results provide an ansatz for the
analytic solution of the problem in the asymptotic limits of weak and strong
coupling.Comment: 8 pages, 3 figures, conference proceedings for the Electron
Correlations and Materials Properties, in Kos, Greece, July 5-9, 200
EffiTest: Efficient Delay Test and Statistical Prediction for Configuring Post-silicon Tunable Buffers
At nanometer manufacturing technology nodes, process variations significantly
affect circuit performance. To combat them, post- silicon clock tuning buffers
can be deployed to balance timing bud- gets of critical paths for each
individual chip after manufacturing. The challenge of this method is that path
delays should be mea- sured for each chip to configure the tuning buffers
properly. Current methods for this delay measurement rely on path-wise
frequency stepping. This strategy, however, requires too much time from ex-
pensive testers. In this paper, we propose an efficient delay test framework
(EffiTest) to solve the post-silicon testing problem by aligning path delays
using the already-existing tuning buffers in the circuit. In addition, we only
test representative paths and the delays of other paths are estimated by
statistical delay prediction. Exper- imental results demonstrate that the
proposed method can reduce the number of frequency stepping iterations by more
than 94% with only a slight yield loss.Comment: ACM/IEEE Design Automation Conference (DAC), June 201
CP violation in semileptonic tau lepton decays
The leading order contribution to the direct CP asymmetry in tau^{+/-} ->
K^{+/-} pi^0 nu_{tau} decay rates is evaluated within the Standard Model. The
weak phase required for CP violation is introduced through an interesting
mechanism involving second order weak interactions, which is also responsible
for tiny violations of the Delta S= Delta Q rule in K_{l3} decays. The
calculated CP asymmetry turns out to be of order 10^{-12}, leaving a large
window for studying effects of non-standard sources of CP violation in this
observable.Comment: 5 pages, 3 figures, version published in Phys.Rev.
Scalable quantum computing with Josephson charge qubits
A goal of quantum information technology is to control the quantum state of a
system, including its preparation, manipulation, and measurement. However,
scalability to many qubits and controlled connectivity between any selected
qubits are two of the major stumbling blocks to achieve quantum computing (QC).
Here we propose an experimental method, using Josephson charge qubits, to
efficiently solve these two central problems. The proposed QC architecture is
scalable since any two charge qubits can be effectively coupled by an
experimentally accessible inductance. More importantly, we formulate an
efficient and realizable QC scheme that requires only one (instead of two or
more) two-bit operation to implement conditional gates.Comment: 4 pages, 2 figure
Phonon-mediated tuning of instabilities in the Hubbard model at half-filling
We obtain the phase diagram of the half-filled two-dimensional Hubbard model
on a square lattice in the presence of Einstein phonons. We find that the
interplay between the instantaneous electron-electron repulsion and
electron-phonon interaction leads to new phases. In particular, a
d-wave superconducting phase emerges when both anisotropic phonons
and repulsive Hubbard interaction are present. For large electron-phonon
couplings, charge-density-wave and s-wave superconducting regions also appear
in the phase diagram, and the widths of these regions are strongly dependent on
the phonon frequency, indicating that retardation effects play an important
role. Since at half-filling the Fermi surface is nested, spin-density-wave is
recovered when the repulsive interaction dominates. We employ a functional
multiscale renormalization-group method that includes both electron-electron
and electron-phonon interactions, and take retardation effects fully into
account.Comment: 8 pages, 5 figure
b-quark decay in the collinear approximation
The semileptonic decay of a b-quark, b--> c l nu, is considered in the
relativistic limit where the decay products are approximately collinear.
Analytic results for the double differential lepton energy distributions are
given for finite charm-quark mass. Their use for the fast simulation of
isolated lepton backgrounds from heavy quark decays is discussed.Comment: 7 pages, 1 figure, submitted to Phys.Rev.
Dynamical Properties of a Growing Surface on a Random Substrate
The dynamics of the discrete Gaussian model for the surface of a crystal
deposited on a disordered substrate is investigated by Monte Carlo simulations.
The mobility of the growing surface was studied as a function of a small
driving force and temperature . A continuous transition is found from
high-temperature phase characterized by linear response to a low-temperature
phase with nonlinear, temperature dependent response. In the simulated regime
of driving force the numerical results are in general agreement with recent
dynamic renormalization group predictions.Comment: 10 pages, latex, 3 figures, to appear in Phys. Rev. E (RC
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