721 research outputs found
Quantum Monte Carlo Study of Pairing Symmetry and Correlation in Iron-based Superconductors
We perform a systematic quantum Monte Carlo study of the pairing correlation
in the symmetric microscopic model for iron-based superconductors. It is
found that the pairing with an extensive s-wave symmetry robustly dominates
over other pairings at low temperature in reasonable parameter region. The
pairing susceptibility, the effective pairing interaction and the
antiferromagnetic correlation strongly increase as the on-site Coulomb
interaction increases, indicating the importance of the effect of
electron-electron correlation. Our non-biased numerical results provide a
unified understanding of superconducting mechanism in iron-pnictides and
iron-chalcogenides and demonstrate that the superconductivity is driven by
strong electron-electron correlation effects.Comment: Accepted for publication as a Letter in Physical Review Letters, and
more discussions are adde
The Abel-Zeilberger Algorithm
We use both Abel's lemma on summation by parts and Zeilberger's algorithm to
find recurrence relations for definite summations. The role of Abel's lemma can
be extended to the case of linear difference operators with polynomial
coefficients. This approach can be used to verify and discover identities
involving harmonic numbers and derangement numbers. As examples, we use the
Abel-Zeilberger algorithm to prove the Paule-Schneider identities, the
Apery-Schmidt-Strehl identity, Calkin's identity and some identities involving
Fibonacci numbers.Comment: 18 page
Three-dimensional numerical study of flow characteristic and membrane fouling evolution in an enzymatic membrane reactor
In order to enhance the understanding of membrane fouling mechanism, the
hydrodynamics of granular flow in a stirred enzymatic membrane reactor was
numerically investigated in the present study. A three-dimensional Euler-Euler
model, coupled with k-e mixture turbulence model and drag function for
interphase momentum exchange, was applied to simulate the two-phase
(fluid-solid) turbulent flow. Numerical simulations of single- or two-phase
turbulent flow under various stirring speed were implemented. The numerical
results coincide very well with some published experimental data. Results for
the distributions of velocity, shear stress and turbulent kinetic energy were
provided. Our results show that the increase of stirring speed could not only
enlarge the circulation loops in the reactor, but it can also increase the
shear stress on the membrane surface and accelerate the mixing process of
granular materials. The time evolution of volumetric function of granular
materials on the membrane surface has qualitatively explained the evolution of
membrane fouling.Comment: 10 panges, 8 figure
Pairing in graphene: A quantum Monte Carlo study
To address the issue of electron correlation driven superconductivity in
graphene, we perform a systematic quantum Monte Carlo study of the pairing
correlation in the t-U-V Hubbard model on a honeycomb lattice. For V=0 and
close to half filling, we find that pairing with d+id symmetry dominates
pairing with extended-s symmetry. However, as the system size or the on-site
Coulomb interaction increases, the long-range part of the d+id pairing
correlation decreases and tends to vanish in the thermodynamic limit. An
inclusion of nearest-neighbor interaction V, either repulsive or attractive,
has a small effect on the extended-s pairing correlation, but strongly
suppresses the d+id pairing correlation.Comment: 5 pages, 5 figure
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