24,864 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
Application of selective epitaxy to fabrication of nanometer scale wire and dot structures
The selective growth of nanometer scale GaAs wire and dot structures using metalorganic vapor phase epitaxy is demonstrated. Spectrally resolved cathodoluminescence images as well as spectra from single dots and wires are presented. A blue shifting of the GaAs peak is observed as the size scale of the wires and dots decreases
Decoherence of flux qubits due to 1/f flux noise
We have investigated decoherence in Josephson-junction flux qubits. Based on
the measurements of decoherence at various bias conditions, we discriminate
contributions of different noise sources. In particular, we present a Gaussian
decay function of the echo signal as evidence of dephasing due to flux
noise whose spectral density is evaluated to be about /Hz
at 1 Hz. We also demonstrate that at an optimal bias condition where the noise
sources are well decoupled the coherence observed in the echo measurement is
mainly limited by energy relaxation of the qubit.Comment: 4 pages, error in Fig.4 corrected, to appear in PR
Semimetalic graphene in a modulated electric potential
The -electronic structure of graphene in the presence of a modulated
electric potential is investigated by the tight-binding model. The low-energy
electronic properties are strongly affected by the period and field strength.
Such a field could modify the energy dispersions, destroy state degeneracy, and
induce band-edge states. It should be noted that a modulated electric potential
could make semiconducting graphene semimetallic, and that the onset period of
such a transition relies on the field strength. There exist infinite
Fermi-momentum states in sharply contrast with two crossing points (Dirac
points) for graphene without external fields. The finite density of states
(DOS) at the Fermi level means that there are free carriers, and, at the same
time, the low DOS spectrum exhibits many prominent peaks, mainly owing to the
band-edge states.Comment: 12pages, 5 figure
Crystallization and preliminary crystallographic analysis of the DNA gyrase B protein from B-stearothermophilus
DNA gyrase B (GyrB) from B. stearothermophilus has been crystallized in the presence of the non-hydrolyzable ATP analogue, 5'-adenylpl-beta-gamma-imidodiphosphate (ADPNP), by the dialysis method. A complete native data set to 3.7 Angstrom has been collected from crystals which belonged to the cubic space group I23 with unit-cell dimension a = 250.6 Angstrom. Self-rotation function analysis indicates the position of a molecular twofold axis. Low-resolution data sets of a thimerosal and a selenomethionine derivative have also been analysed. The heavy-atom positions are consistent with one dimer in the asymmetric unit
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
Fixação simbiótica de nitrogênio em soja cultivada em perlita e suplementada com silicato de sódio.
bitstream/item/66222/1/32018.pdfFERTBI
Detection of mechanical resonance of a single-electron transistor by direct current
We have suspended an Al based single-electron transistor whose island can
resonate freely between the source and drain leads forming the clamps. In
addition to the regular side gate, a bottom gate with a larger capacitance to
the SET island is placed underneath to increase the SET coupling to mechanical
motion. The device can be considered as a doubly clamped Al beam that can
transduce mechanical vibrations into variations of the SET current. Our
simulations based on the orthodox model, with the SET parameters estimated from
the experiment, reproduce the observed transport characteristics in detail.Comment: 4 pages, 3 figure
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