8,348 research outputs found
Comparative Study of BCS-BEC Crossover Theories above : the Nature of the Pseudogap in Ultra-Cold Atomic Fermi Gases
This paper presents a comparison of two finite-temperature BCS-Bose Einstein
condensation (BEC) crossover theories above the transition temperature:
Nozieres Schmitt-Rink (NSR) theory and finite -extended BCS-Leggett theory.
The comparison is cast in the form of numerical studies of the behavior of the
fermionic spectral function both theoretically and as constrained by
(primarily) radio frequency (RF) experiments. Both theories include pair
fluctuations and exhibit pseudogap effects, although the nature of this
pseudogap is very different. The pseudogap in finite -extended BCS-Leggett
theory is found to follow a BCS-like dispersion which, in turn, is associated
with a broadened BCS-like self energy, rather more similar to what is observed
in high temperature superconductors (albeit, for a d-wave case). The fermionic
quasi-particle dispersion is different in NSR theory and the damping is
considerably larger. We argue that the two theories are appropriate in
different temperature regimes with the BCS-Leggett approach more suitable
nearer to condensation. There should, in effect, be little difference at higher
as the pseudogap becomes weaker and where the simplifying approximations
used in the BCS-Leggett approach break down. On the basis of
momentum-integrated radio frequency studies of unpolarized gases, it would be
difficult to distinguish which theory is the better. A full comparison for
polarized gases is not possible since there is claimed to be inconsistencies in
the NSR approach (not found in the BCS-Leggett scheme). Future experiments
along the lines of momentum resolved experiments look to be very promising in
distinguishing the two theories.Comment: 16 pages, 11 figure
Charge Ordered RVB States in the Doped Cuprates
We study charge ordered d-wave resonating valence bond states (dRVB) in the
doped cuprates, and estimate the energies of these states in a generalized model by using a renormalized mean field theory. The long range Coulomb
potential tends to modulate the charge density in favor of the charge ordered
RVB state. The possible relevance to the recently observed
checkerboard patterns in tunnelling conductance in high cuprates is
discussed.Comment: 4 pages, 4 figures, 3 table
Effect of pmma-mwnts loading on Co2 separation performance of thin film nanocomposite membrane
Nanocomposite membrane, especially the thin film nanocomposite (TFN) fabricated via interfacial polymerization (IP) is a relatively new class of membrane which features good separation performance and practical processing. This study investigated on the effects of multi-walled carbon nanotubes (MWNTs) loading on the gas separation performance of the resultant TFNs. TFNs were tested with pure CO2, N2 and CH4 gases at feed pressure of 2 bar. The findings from this study suggested that the optimum fillers loading was around 0.25 g/L in the coating solution which gives TFN with CO2 permeance of 53.5 gas permeation unit (GPU) (12% higher than base membrane without filler), CO2/N2 selectivity of 61 and CO2/CH4 selectivity of 35. The enhancement in CO2 permeance without sacrificing the membrane selectvities was attributed to the good dispersion and compatibility of the MWNTs with the polymer matrix while the nanotubes serve as rapid diffusion channels to facilitate transport of gases. TFN embedded with polymethyl methacrylate (PMMA)-MWNTs showed potential for low pressure carbon capture and storage application
High speed quantum gates with cavity quantum electrodynamics
Cavity quantum electrodynamic schemes for quantum gates are amongst the
earliest quantum computing proposals. Despite continued progress, and the
dramatic recent demonstration of photon blockade, there are still issues with
optimal coupling and gate operation involving high-quality cavities. Here we
show dynamic control techniques that allow scalable cavity-QED based quantum
gates, that use the full bandwidth of the cavities. When applied to quantum
gates, these techniques allow an order of magnitude increase in operating
speed, and two orders of magnitude reduction in cavity Q, over passive
cavity-QED architectures. Our methods exploit Stark shift based Q-switching,
and are ideally suited to solid-state integrated optical approaches to quantum
computing.Comment: 4 pages, 3 figures, minor revision
The Neutrino Magnetic Moment Induced by Leptoquarks
Allowing leptoquarks to interact with both right-handed and left-handed
neutrinos (i.e., ``non-chiral'' leptoquarks), we show that a non-zero neutrino
magnetic moment can arise naturally. Although the mass of the non-chiral vector
leptoquark that couples to the first generation fermions is constrained
severely by universality of the leptonic decays and is found to be
greater than 50 TeV, the masses of the second and third generation non-chiral
vector leptoquarks may evade such constraint and may in general be in the range
of TeV. With reasonable input mass and coupling values, we find
that the neutrino magnetic moment due to the second generation leptoquarks is
of the order of while that caused by the
third generation leptoquarks, being enhanced significantly by the large top
quark mass, is in the range of .Comment: 11 pages, 3 eps figures, uses revte
Unified theory for Goos-H\"{a}nchen and Imbert-Fedorov effects
A unified theory is advanced to describe both the lateral Goos-H\"{a}nchen
(GH) effect and the transverse Imbert-Fedorov (IF) effect, through representing
the vector angular spectrum of a 3-dimensional light beam in terms of a 2-form
angular spectrum consisting of its 2 orthogonal polarized components. From this
theory, the quantization characteristics of the GH and IF displacements are
obtained, and the Artmann formula for the GH displacement is derived. It is
found that the eigenstates of the GH displacement are the 2 orthogonal linear
polarizations in this 2-form representation, and the eigenstates of the IF
displacement are the 2 orthogonal circular polarizations. The theoretical
predictions are found to be in agreement with recent experimental results.Comment: 15 pages, 3 figure
Very Long Baseline Neutrino Oscillation Experiment for Precise Measurements of Mixing Parameters and CP Violating Effects
We analyze the prospects of a feasible, Brookhaven National Laboratory based,
very long baseline (BVLB) neutrino oscillation experiment consisting of a
conventional horn produced low energy wide band beam and a detector of 500 kT
fiducial mass with modest requirements on event recognition and resolution.
Such an experiment is intended primarily to determine CP violating effects in
the neutrino sector for 3-generation mixing. We analyze the sensitivity of such
an experiment. We conclude that this experiment will allow determination of the
CP phase and the currently unknown mixing parameter
, if , a value times
lower than the present experimental upper limit. In addition to
and , the experiment has great potential for precise measurements
of most other parameters in the neutrino mixing matrix including , , ,
and the mass ordering of neutrinos through the observation of the matter effect
in the appearance channel.Comment: 12 pages, 10 figure
Active Width at a Slanted Active Boundary in Directed Percolation
The width W of the active region around an active moving wall in a directed
percolation process diverges at the percolation threshold p_c as W \simeq A
\epsilon^{-\nu_\parallel} \ln(\epsilon_0/\epsilon), with \epsilon=p_c-p,
\epsilon_0 a constant, and \nu_\parallel=1.734 the critical exponent of the
characteristic time needed to reach the stationary state \xi_\parallel \sim
\epsilon^{-\nu_\parallel}. The logarithmic factor arises from screening of
statistically independent needle shaped sub clusters in the active region.
Numerical data confirm this scaling behaviour.Comment: 5 pages, 5 figure
Evidence of metallic clustering in annealed Ga1-xMnxAs from atypical scaling behavior of the anomalous Hall coefficient
We report on the anomalous Hall coefficient and longitudinal resistivity
scaling relationships on a series of annealed Ga1-xMnxAs epilayers (x~0.055).
As-grown samples exhibit scaling parameter n of ~ 1. Near the optimal annealing
temperature, we find n ~ 2 to be consistent with recent theories on the
intrinsic origins of anomalous Hall Effect in Ga1-xMnxAs. For annealing
temperatures far above the optimum, we note n > 3, similar behavior to certain
inhomogeneous systems. This observation of atypical behavior agrees well with
characteristic features attributable to spherical resonance from metallic
inclusions from optical spectroscopy measurements.Comment: 3 pages, 3 figure
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