414 research outputs found
Sectional symmetry of solutions of elliptic systems in cylindrical domains
In this paper we prove a kind of rotational symmetry for solutions of semilinear elliptic systems in some bounded cylindrical domains. The symmetry theorems obtained hold for low-Morse index solutions whenever the nonlinearities satisfy some convexity assumptions. These results extend and improve those obtained in [6, 9, 16, 18]
Elusive electron-phonon coupling in quantitative analyses of the spectral function
We examine multiple techniques for extracting information from angle-resolved
photoemission spectroscopy (ARPES) data, and test them against simulated
spectral functions for electron-phonon coupling. We find that, in the
low-coupling regime, it is possible to extract self-energy and bare-band
parameters through a self-consistent Kramers-Kronig bare-band fitting routine.
We also show that the effective coupling parameters deduced from the
renormalization of quasiparticle mass, velocity, and spectral weight are
momentum dependent and, in general, distinct from the true microscopic
coupling; the latter is thus not readily accessible in the quasiparticle
dispersion revealed by ARPES.Comment: A high-resolution version can be found at
http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/KKBF.pd
Strong spin-orbit coupling effects on the Fermi surface of Sr2RuO4 and Sr2RhO4
We present a first-principle study of spin-orbit coupling effects on the
Fermi surface of Sr2RuO4 and Sr2RhO4. For nearly degenerate bands, spin-orbit
coupling leads to a dramatic change of the Fermi surface with respect to
non-relativistic calculations; as evidenced by the comparison with experiments
on Sr2RhO4, it cannot be disregarded. For Sr2RuO4, the Fermi surface
modifications are more subtle but equally dramatic in the detail: spin-orbit
coupling induces a strong momentum dependence, normal to the RuO2 planes, for
both orbital and spin character of the low-energy electronic states. These
findings have profound implications for the understanding of unconventional
superconductivity in Sr2RuO4.Comment: A high-resolution version can be found at
http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/SO_Sr2RuO4.pd
Inversion symmetry in the spin-Peierls compound NaV2O5
At room-temperature NaV2O5 was found to have the centrosymmetric space group
Pmmn. This space group implies the presence of only one kind of V site in
contrast with previous reports of the non-centrosymmetric counterpart P21mn.
This indicates a non-integer valence state of vanadium.
Furthermore, this symmetry has consequences for the interpretation of the
transition at 34 K, which was ascribed to a spin-Peierls transition of one
dimensional chains of V4+.Comment: Revtex, 3 pages, 2 postscript pictures embedded in the text.
Corrected a mistake in one pictur
Low temperature ellipsometry of NaV2O5
The dielectric function of alpha'NaV2O5 was measured with electric field
along the a and b axes in the photon energy range 0.8-4.5 eV for temperatures
down to 4K. We observe a pronounced decrease of the intensity of the 1 eV peak
upon increasing temperature with an activation energy of about 25meV,
indicating that a finite fraction of the rungs becomes occupied with two
electrons while others are emptied as temperature increases. No appreciable
shifts of peaks were found s in the valence state of individual V atoms at the
phase transition is very small. A remarkable inflection of this temperature
dependence at the phase transition at 34 K indicates that charge ordering is
associated with the low temperature phase.Comment: Revisions in style and order of presentation. One new figure. In
press in Physical Review B. REVTeX, 4 pages with 4 postscript figure
Infrared optical properties of the spin-1/2 quantum magnet
We report results on the electrodynamic response of , a
low-dimensional spin-1/2 quantum magnet that shows a spin gap formation for
T= 67 . The Fano-like shape of a few selected infrared active
phonons suggests an interaction between lattice vibrations and a continuum of
low frequency (spin) excitations. The temperature dependence of the phonon mode
parameters extends over a broad temperature range well above ,
indicating the presence of an extended fluctuation regime. In the temperature
interval between 200 and there is a progressive dimensionality
crossover (from two to one), as well as a spectral weight shift from low
towards high frequencies. This allows us to identify a characteristic energy
scale of about 430 , ascribed to a pseudo spin-gap
Anomalous high energy dispersion in photoemission spectra from insulating cuprates
Angle resolved photoelectron spectroscopic measurements have been performed
on an insulating cuprate Ca_2CuO_2Cl_2. High resolution data taken along the
\Gamma to (pi,pi) cut show an additional dispersive feature that merges with
the known dispersion of the lowest binding energy feature, which follows the
usual strongly renormalized dispersion of ~0.35 eV. This higher energy part
reveals a dispersion that is very close to the unrenormalized band predicted by
band theory. A transfer of spectral weight from the low energy feature to the
high energy feature is observed as the \Gamma point is approached. By comparing
with theoretical calculations the high energy feature observed here
demonstrates that the incoherent portion of the spectral function has
significant structure in momentum space due to the presence of various energy
scales.Comment: 5 pages, 3 figure
BCS-BEC crossover at finite temperature for superfluid trapped Fermi atoms
We consider the BCS-BEC crossover for a system of trapped Fermi atoms at
finite temperature, both below and above the superfluid critical temperature,
by including fluctuations beyond mean field. We determine the superfluid
critical temperature and the pair-breaking temperature as functions of the
attractive interaction between Fermi atoms, from the weak- to the
strong-coupling limit (where bosonic molecules form as bound-fermion pairs).
Density profiles in the trap are also obtained for all temperatures and
couplings.Comment: revised version, to be published in Phys. Rev. Let
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