2,589 research outputs found
Signature of antiferromagnetic long-range order in the optical spectrum of strongly correlated electron systems
We show how the onset of a non-Slater antiferromagnetic ordering in a
correlated material can be detected by optical spectroscopy. Using dynamical
mean-field theory we identify two distinctive features: The antiferromagnetic
ordering is associated with an enhanced spectral weight above the optical gap,
and well separated spin-polaron peaks emerge in the optical spectrum. Both
features are indeed observed in LaSrMnO_4 [G\"ossling et al., Phys. Rev. B 77,
035109 (2008)]Comment: 11 pages, 9 figure
Temperature dependence of the optical spectral weight in the cuprates: Role of electron correlations
We compare calculations based on the Dynamical Mean-Field Theory of the
Hubbard model with the infrared spectral weight of
LaSrCuO and other cuprates. Without using fitting parameters we
show that most of the anomalies found in with respect to normal
metals, including the existence of two different energy scales for the doping-
and the -dependence of , can be ascribed to strong correlation
effects.Comment: 4 pages, 3 figures. Minor corrections, corrected some typos and added
reference
Effect of mesoscopic inhomogeneities on local tunnelling density of states
We carry out a theoretical analysis of the momentum dependence of the
Fourier-transformed local density of states (LDOS) in the superconducting
cuprates within a model considering the interference of quasiparticles
scattering on quenched impurities. The impurities introduce an external
scattering potential, which is either nearly local in space or it can acquire a
substantial momentum dependence due to a possible strong momentum dependence of
the electronic screening near a charge modulation instability. The key new
effect that we introduce is an additional mesoscopic disorder aiming to
reproduce the inhomogeneities experimentally observed in scanning tunnelling
microscopy. The crucial effect of this mesoscopic disorder is to give rise to
point-like spectroscopic features, to be contrasted with the curve-like shape
of the spectra previously calculated within the interfering-quasiparticle
schemes. It is also found that stripe-like charge modulations play a relevant
role to correctly reproduce all the spectral features of the experiments.Comment: 11 pages and 5 figure
Anomalous impurity effects in nonadiabatic superconductors
We show that, in contrast with the usual electron-phonon Migdal-Eliashberg
theory, the critical temperature Tc of an isotropic s-wave nonadiabatic
superconductor is strongly reduced by the presence of diluted non-magnetic
impurities. Our results suggest that the recently observed Tc-suppression
driven by disorder in K3C60 [Phys. Rev. B vol.55, 3866 (1997)] and in
Nd(2-x)CexCuO(4-delta) [Phys. Rev. B vol.58, 8800 (1998)] could be explained in
terms of a nonadiabatic electron-phonon coupling. Moreover, we predict that the
isotope effect on Tc has an impurity dependence qualitatively different from
the one expected for anisotropic superconductors.Comment: 10 pages, euromacr.tex, europhys.sty, 6 figures. Replaced with
accepted version (Europhysics Letters
An assessment of the effect of supersonic aircraft operations on the stratospheric ozone content
An assessment of the potential effect on stratospheric ozone of an advanced supersonic transport operations is presented. This assessment, which was undertaken because of NASA's desire for an up-to-date evaluation to guide programs for the development of supersonic technology and improved aircraft engine designs, uses the most recent chemical reaction rate data. From the results of the present assessment it would appear that realistic fleet sizes should not cause concern with regard to the depletion of the total ozone overburden. For example, the NOx emission of one type designed to cruise at 20 km altitude will cause the ozone overburden to increase by 0.03% to 0.12%, depending upon which vertical transport is used. These ozone changes can be compared with the predictions of a 1.74% ozone decrease (for 100 Large SST's flying at 20 km) made in 1974 by the FAA's Climatic Impact Assessment Program
Kinks: Fingerprints of strong electronic correlations
The textbook knowledge of solid state physics is that the electronic specific
heat shows a linear temperature dependence with the leading corrections being a
cubic term due to phonons and a cubic-logarithmic term due to the interaction
of electrons with bosons. We have shown that this longstanding conception needs
to be supplemented since the generic behavior of the low-temperature electronic
specific heat includes a kink if the electrons are sufficiently strongly
correlatedComment: 4 pages, 1 figure, ICM 2009 conference proceedings (to appear in
Journal of Physics: Conference Series
Environmental effects of SPS: The middle atmosphere
The heavy lift launch vehicle associated with the solar power satellite (SPS) would deposit in the upper atmosphere exhaust and reentry products which could modify the composition of the stratosphere, mesosphere, and lower ionosphere. In order to assess such effects, atmospheric model simulations were performed, especially considering a geographic zone centered at the launch and reentry latitudes
Resonating bipolarons
Electrons coupled to local lattice deformations end up in selftrapped
localized molecular states involving their binding into bipolarons when the
coupling is stronger than a certain critical value. Below that value they exist
as essentially itinerant electrons. We propose that the abrupt crossover
between the two regimes can be described by resonant pairing similar to the
Feshbach resonance in binary atomic collision processes. Given the
intrinsically local nature of the exchange of pairs of itinerant electrons and
localized bipolarons, we demonstrate the occurrence of such a resonance on a
finite-size cluster made out of metallic atoms surrounding a polaronic ligand
center.Comment: 7 pages, 4 figures, to be published in Europhysics Letter
Two-dimensional model studies of the effect of supersonic aircraft operations on the stratospheric ozone content
For a fleet of 250 aircraft, the change in the ozone column is predicted to be very close to zero; in fact, the ozone overburden may actually increase as a result of show that above 25 to 30 km the ozone abundance decreases via catalytic destruction, but at lower heights it increases, mainly as a result of coupling with odd hydrogen species. Water vapor released in the engine exhaust is predicted to cause ozone decreases; for the hypothetical engines used in the study, the total column ozone changes due to water vapor emission largely offset the predicted ozone increases due to NOx emission. The actual effect of water vapor may be less than calculated because present models do not include thermal feedback. Feedback refers to the cooling effect of additional water vapor that would tend to slow the NOx reactions which destroy ozone
Pairing and superconductivity from weak to strong coupling in the attractive Hubbard model
Comment: 10 pages, 8 figure
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