434 research outputs found
From Cooper Pairs to Composite Bosons: A Generalized RPA Analysis of Collective Excitations
The evolution of the ground state and the excitation spectrum of the two and
three dimensional attractive Hubbard model is studied as the system evolves
from a Cooper pair regime for weak attraction to a composite boson regime for a
strong attraction.Comment: 20 pages RevTex, 7 figures on reques
Half-Integral Spin-Singlet Quantum Hall Effect
We provide numerical evidence that the ground state of a short range
interaction model at is incompressible and spin-singlet for a wide
range of repulsive interactions. Furthermore it is accurately described by a
trial wave function studied earlier. For the Coulomb interaction we find that
this wave function provides a good description of the lowest lying spin-singlet
state, and propose that fractional quantum Hall effect would occur at
if this state became the global ground state.Comment: Latex 13 pages, 3 figures upon reques
Possibility of p-wave pairing of composite fermions at
We find that for the pure Coulomb repulsion the composite Fermi sea at
is on the verge of an instability to triplet pairing of composite
fermions. It is argued that a transition into the paired state, described by a
Pfaffian wave function, may be induced if the short-range part of the
interaction is softened by increasing the thickness of the two-dimensional
electron system.Comment: 14 pages, 3 eps figures include
Charge Density Wave in Two-Dimensional Electron Liquid in Weak Magnetic Field
We study the ground state of a clean two-dimensional electron liquid in a
weak magnetic field where lower Landau levels are completely filled
and the upper level is partially filled. It is shown that the electrons at the
upper Landau level form domains with filling factor equal to one and zero. The
domains alternate with a spatial period of order of the cyclotron radius, which
is much larger than the interparticle distance at the upper Landau level. The
one-particle density of states, which can be probed by tunneling experiments,
is shown to have a pseudogap linearly dependent on the magnetic field in the
limit of large .Comment: Several errors correcte
Deviations from Fermi-liquid behavior above in 2D short coherence length superconductors
We show that there are qualitative differences between the temperature
dependence of the spin and charge correlations in the normal state of the 2D
attractive Hubbard model using quantum Monte Carlo simulations. The
one-particle density of states shows a pseudogap above \tc with a depleted
with decreasing . The susceptibility \cs and the low frequency spin
spectral weight track , which explains the spin-gap scaling: 1/T_1T \sim
\cs(T). However the charge channel is dominated by collective behavior and the
compressibility is -independent. This anomalous ``spin-charge
separation'' is shown to exist even at intermediate where the momentum
distribution n(\bk) gives evidence for degenerate Fermi system.Comment: 4 pages (twocolumn format), 5 Postscript figure
Quantum Hall effect in single wide quantum wells
We study the quantum Hall states in the lowest Landau level for a single wide
quantum well. Due to a separation of charges to opposite sides of the well, a
single wide well can be modelled as an effective two level system. We provide
numerical evidence of the existence of a phase transition from an
incompressible to a compressible state as the electron density is increased for
specific well width. Our numerical results show a critical electron density
which depends on well width, beyond which a transition incompressible double
layer quantum Hall state to a mono-layer compressible state occurs. We also
calculate the related phase boundary corresponding to destruction of the
collective mode energy gap. We show that the effective tunneling term and the
interlayer separation are both renormalised by the strong magnetic field. We
also exploite the local density functional techniques in the presence of strong
magnetic field at to calculate renormalized . The
numerical results shows good agreement between many-body calculations and local
density functional techniques in the presence of a strong magnetic field at
. we also discuss implications of this work on the
incompressible state observed in SWQW.Comment: 30 pages, 7 figures (figures are not included
Nonperturbative XY-model approach to strong coupling superconductivity in two and three dimensions
For an electron gas with delta-function attraction we investigate the
crossover from weak- to strong-coupling supercoductivity in two and three
dimensions. We derive analytic expressions for the stiffness of phase
fluctuations and set up effective XY-models which serve to determine
nonperturbatively the temperature of phase decoherence where superconductivity
breaks down. We find the transition temperature T_c as a monotonous function of
the coupling strength and carrier density both in two and three dimensions, and
give analytic formulas for the merging of the temperature of phase decoherence
with the temperature of pair formation in the weak-coupling limit.Comment: Few typos corrected. Emails that were sent to the address
[email protected] in June and July 1999 were lost in a computer crash, so if
your comments were not answered please send them once mor
Two - Dimensional Electron Liquid in a Weak Magnetic Field
We present an effective theory describing the low-energy properties of an
interacting 2D electron gas at large non-integer filling factors .
Assuming that the interaction is sufficiently weak, , we integrate out
all the fast degrees of freedom, and derive the effective Hamiltonian acting in
the Fock space of the partially filled Landau level only. This theory enables
us to find two energy scales controlling the electron dynamics at energies less
than . The first energy scale, , appears in the one electron spectral density as the width of a
pseudogap. The second scale, , is parametrically larger; it
characterizes the exchange-enhanced spin splitting and the thermodynamic
density of states.Comment: Submitted in Phys. Rev. B, 30 pages, 3 figures upon reques
The Ground State of a Two-Dimensional Electron Liquid in a Weak Magnetic Field
We study the ground state of a clean two-dimensional electron liquid in a
weak magnetic field where lower Landau levels are completely filled
and the upper level is partially filled. It is shown that the electrons at the
upper Landau level form domains with filling factor equal to one and zero. The
domains alternate with a spatial period of the order of the cyclotron radius,
which is much larger than the interparticle distance at the upper Landau level.
The one-particle density of states, which can be probed by tunneling
experiments, is shown to have a pseudogap linearly dependent on the magnetic
field in the limit of large .Comment: REVTeX, 21 pages + 12 figures in PostScript. Uses amsfonts.sty,
multicol.sty, and psfig.st
Contrasting patterns of genetic and phenotypic differentiation in two invasive salmonids in the southern hemisphere
Peer reviewe
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