18,690 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
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
On Analytic Properties of the Photon Polarization Function in a Background Magnetic Field
We examine the analytic properties of the photon polarization function in a
background magnetic field, using the technique of inverse Mellin transform. The
photon polarization function is first expressed as a power series of the photon
energy with . Based upon this energy expansion and the
branch cut of the photon polarization function in the complex plane,
we compute the absorptive part of the polarization function with the inverse
Mellin transform. Our results are valid for arbitrary photon energies and
magnetic-field strengths. The applications of our approach are briefly
discussed.Comment: Revtex, 8 pages; Eq. (33) corrected, results of the paper not
affecte
Weak dipole moment of in collisions with longitudinally polarized electrons
It is pointed out that certain CP-odd momentum correlations in the production
and subsequent decay of tau pairs in collisions get enhanced when the
is longitudinally polarized. Analytic expressions for these correlations
are obtained for the single-pion decay mode of when have
a ``weak" dipole form factor (WDFF) coupling to . For collisions
at the peak, a sensitivity of about 1-5\mbox{ cm} for
the WDFF can be reached using a {\em single} decay
channel, with 's likely to be available at the SLC at Stanford with
polarization of 62\%-75\%.Comment: 9 pages, Latex, PRL-TH-93/17 (Revised
Broken time-reversal symmetry in Josephson junction involving two-band superconductors
A novel time-reversal symmetry breaking state is found theoretically in the
Josephson junction between the two-gap superconductor and the conventional
s-wave superconductor. This occurs due to the frustration between the three
order parameters analogous to the two antiferromagnetically coupled XY-spins
put under a magnetic field. This leads to the interface states with the
energies inside the superconducting gap. Possible experimental observations of
this state with broken time-reversal symmetry are discussed.Comment: 9 pages, 1 figur
Self-energy corrections to anisotropic Fermi surfaces
The electron-electron interactions affect the low-energy excitations of an
electronic system and induce deformations of the Fermi surface. These effects
are especially important in anisotropic materials with strong correlations,
such as copper oxides superconductors or ruthenates. Here we analyze the
deformations produced by electronic correlations in the Fermi surface of
anisotropic two-dimensional systems, treating the regular and singular regions
of the Fermi surface on the same footing. Simple analytical expressions are
obtained for the corrections, based on local features of the Fermi surface. It
is shown that, even for weak local interactions, the behavior of the
self-energy is non trivial, showing a momentum dependence and a self-consistent
interplay with the Fermi surface topology. Results are compared to experimental
observations and to other theoretical results.Comment: 13 pages, 10 figure
Enhancement of Si-O hybridization in low-temperature grown ultraviolet photo-oxided SiO2 film observed by x-ray absorption and photoemission spectroscopy
100學年度杜昭宏升等參考著作[[abstract]]The dielectric properties associated with the electronic and bonding structures of SiO2 films were examined using the Si L3,2- and O K-edge x-ray absorption near-edge structures (XANES) and valence-band photoemission spectroscopy (VB-PES) techniques. The Si L3,2- and O K-edge XANES measurements for the low-temperature grown UV-photon oxidized SiO2 (UV-SiO2) and the conventional high-temperature thermal-oxidized SiO2 (TH-SiO2) suggest enhancement of O 2p–Si 3p hybridization in UV-SiO2. VB-PES measurements reveal enhancement of nonbonding O 2p and O 2p–Si 3p hybridized states. The enhanced O 2p and Si 3p hybridization implies a shortening of the average Si–O bond length, which explains an increase of the density and the improvement of the dielectric property of UV-SiO2.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]紙
Electronic and bonding structures of amorphous Si–C–N thin films by x-ray absorption spectroscopy
[[abstract]]X-ray absorption near edge structure (XANES) spectra of hard amorphous a-Si–C–N thin films with various compositions were measured at the C and N K-edge using sample drain current and fluorescent modes. The C K-edge XANES spectra of a-Si–C–N contain a relatively large 1s→π∗ peak, indicating that a substantial percentage of carbon atoms in the a-Si–C–N films have sp2 or graphite-like bonding. Both the observed sp2 intensity and the Young’s modulus decrease with an increase in the carbon content. For N K-edge XANES spectra of the a-Si–C–N films we find the emergence of a sharp peak near the threshold when the carbon content is larger than between 9% and 36%, which indicates that carbon and nitrogen atoms tend to form local graphitic carbon nitride.[[booktype]]紙
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