1,625 research outputs found
The vortex state in the BEC to BCS crossover: a path-integral description
We derive a path-integral description of the vortex state of a fermionic
superfluid in the crossover region between the molecular condensate (BEC)
regime and the Cooper pairing (BCS) regime. This path-integral formalism,
supplemented by a suitable choice for the saddle point value of the pairing
field in the presence of a vortex, offers a unified description that
encompasses both the BEC and BCS limits. The vortex core size is studied as a
function of the tunable interaction strength between the fermionic atoms. We
find that in the BEC regime, the core size is determined by the molecular
healing length, whereas in the BCS regime, the core size is proportional only
to the Fermi wave length. The observation of such quantized vortices in dilute
Fermi gases would provide an unambiguous proof of the realization of
superfluidity in these gases.Comment: 10 pages, 2 figure
BCS-to-BEC crossover from the exact BCS solution
The BCS-to-BEC crossover, as well as the nature of Cooper pairs, in a
superconducting and Fermi superfluid medium is studied from the exact ground
state wavefunction of the reduced BCS Hamiltonian. As the strength of the
interaction increases, the ground state continuously evolves from a
mixed-system of quasifree fermions and pair resonances (BCS), to pair
resonances and quasibound molecules (pseudogap), and finally to a system of
quasibound molecules (BEC). A single unified scenario arises where the
Cooper-pair wavefunction has a unique functional form. Several exact analytic
expressions, such as the binding energy and condensate fraction, are derived.
We compare our results with recent experiments in ultracold atomic Fermi gases.Comment: 5 pages, 4 figures. Revised version with one figure adde
Numerical Evidence of Luttinger and Fermi Liquid Behaviour in the 2D Hubbard Model
The two dimensional Hubbard model with a single spin-up electron interacting
with a finite density of spin-down electrons is studied using the quantum
Monte Carlotechnique, a new conjugate gradient method for the evaluation of
the Edwards wavefunction ansatz, and the standard second order perturbation
theory. We performed simulations up to 242 sites at reaching the zero
temperature properties with no ``fermion sign problem'' and found a
surprisingly good accuracy of the Edwards wavefunction ansatz at low density or
low doping. The conjugate gradient method was then applied to system up to 1922
sites and infinite for the Edwards state. Fermi liquid theory seems to
remain stable in 2D for all cases studied with the exception of the half
filling case where a ``Luttinger like behavior'' survives in the Hubbard model
, yielding a vanishing quasiparticle weight in the thermodynamic limit.Comment: 10 pages + 4 pictures, RevTex, SISSA 121/93/CM/M
One-Particle Excitation of the Two-Dimensional Hubbard Model
The real part of the self-energy of interacting two-dimensional electrons has
been calculated in the t-matrix approximation. It is shown that the forward
scattering results in an anomalous term leading to the vanishing
renormalization factor of the one-particle Green function, which is a
non-perturbative effect of the interaction U. The present result is a
microscopic demonstration of the claim by Anderson based on the conventional
many-body theory. The effect of the damping of the interacting electrons, which
has been ignored in reaching above conclusion, has been briefly discussed.Comment: 7 pages, LaTeX, 1 figure, uses jpsj.sty, to be published in J. Phys.
Soc. Jpn. 66 No. 3 (1997
Density-induced BCS to Bose-Einstein crossover
We investigate the zero-temperature BCS to Bose-Einstein crossover at the
mean-field level, by driving it with the attractive potential and the particle
density.We emphasize specifically the role played by the particle density in
this crossover.Three different interparticle potentials are considered for the
continuum model in three spatial dimensions, while both s- and d-wave solutions
are analyzed for the attractive (extended) Hubbard model on a two-dimensional
square lattice. For this model the peculiar behavior of the crossover for the
d-wave solution is discussed.In particular, in the strong-coupling limit when
approaching half filling we evidence the occurrence of strong correlations
among antiparallel-spin fermions belonging to different composite bosons, which
give rise to a quasi-long-range antiferromagnetic order in this limit.Comment: 10 pages, 5 enclosed figure
Spin-Charge Separation, Anomalous Scaling and the Coherence of Hopping in exactly solved Two Chain Models
The coherence of transport between two one-dimensional interacting Fermi
liquids, coupled by single particle hopping and interchain interaction, is
examined in the context of two exactly soluble models. It is found that the
coherence of the inter-chain hopping depends on the interplay between
inter-chain hopping and inter-chain interaction terms, and not simply on the
ground state spectral properties of an isolated chain. Specifically, the
splitting of levels in associated with interchain hopping in a soluble
model is found to be enhanced by the introduction of interchain interaction. It
is also shown that, for an exactly solvable model with both and
interactions, coherent interchain hopping coexists with anomalous scaling and
non-Fermi liquid behavior in the chain direction.Comment: Two postscript figure
Decay of escherichia coli in soil following the application of biosolids to agricultural land
The decay of Escherichia coli in a sandy loam soil, amended with enhanced and conventionally treated biosolids, was investigated in a field experiment following spring and autumn applications of sewage sludge. Control soils, without the application of biosolids, were also examined to determine the background indigenous populations of E. coli which are present in the environment. The survival of indigenous E. coli and populations of E. coli applied to soil in biosolids, is assessed in relation to environmental factors influencing pathogen-decay processes in soil
Ferromagnetism in the two dimensional t-t' Hubbard model at the Van Hove density
Using an improved version of the projection quantum Monte Carlo technique, we
study the square-lattice Hubbard model with nearest-neighbor hopping t and
next-nearest-neighbor hopping t', by simulation of lattices with up to 20 X 20
sites. For a given R=2t'/t, we consider that filling which leads to a singular
density of states of the noninteracting problem. For repulsive interactions, we
find an itinerant ferromagnet (antiferromagnet) for R=0.94 (R=0.2). This is
consistent with the prediction of the T-matrix approximation, which sums the
most singular set of diagrams.Comment: 10 pages, RevTeX 3.0 + a single postscript file with all figure
Theory of the temperature and doping dependence of the Hall effect in a model with x-ray edge singularities in d=oo
We explain the anomalous features in the Hall data observed experimentally in
the normal state of the high-Tc superconductors. We show that a consistent
treatment of the local spin fluctuations in a model with x-ray edge
singularities in d=oo reproduces the temperature and the doping dependence of
the Hall constant as well as the Hall angle in the normal state. The model has
also been invoked to justify the marginal-Fermi-liquid behavior, and provides a
consistent explanation of the Hall anomalies for a non-Fermi liquid in d=oo.Comment: 5 pages, 4 figures, To appear in Phys. Rev. B, title correcte
Quasi-Particles in Two-Dimensional Hubbard Model: Splitting of Spectral Weight
It is shown that the energy and momentum dependences of
the electron self-energy function are, where is some
constant, being the band energy,
and the critical exponent , which depends on the curvature of the
Fermi surface at , satisfies, . This leads to a
new type of electron liquid, which is the Fermi liquid in the limit of but for has a split
one-particle spectra as in the Tomonaga-Luttinger liquid.Comment: 8 pages (LaTeX) 4 figures available upon request will be sent by air
mail. KomabaCM-preprint-O
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