172,272 research outputs found
Hot Spots and Pseudogaps for Hole- and Electron-Doped High-Temperature Superconductors
Using cluster perturbation theory, it is shown that the spectral weight and
pseudogap observed at the Fermi energy in recent Angle Resolved Photoemission
Spectroscopy (ARPES) of both electron and hole-doped high-temperature
superconductors find their natural explanation within the t-t'-t''-U Hubbard
model in two dimensions. The value of the interaction U needed to explain the
experiments for electron-doped systems at optimal doping is in the weak to
intermediate coupling regime where the t-J model is inappropriate. At strong
coupling, short-range correlations suffice to create a pseudogap but at weak
coupling long correlation lengths associated with the antiferromagnetic wave
vector are necessary.Comment: RevTeX 4, 4 pages, 5 figures (2 in color
Competition between Spiral-Defect Chaos and Rolls in Rayleigh-Benard Convection
We present experimental results for pattern formation in Rayleigh-Benard
convection of a fluid with a Prandtl number, Pr~ 4. We find that the
spiral-defect-chaos (SDC) attractor which exists for Pr~1 has become unstable.
Gradually increasing the temperature difference from below to well above its
critical value no longer leads to SDC. A sudden jump of temperature difference
from below to above onset causes convection to grow from thermal fluctuations
and does yield SDC. However, the SDC is a transient; it coarsens and forms a
single cell-filling spiral which then drifts toward the cell wall and
disappears.Comment: 9 pages(RevTeX), 5 jpg figures, To appear as Rapid Communication in
PR
London force and energy transportation between interfacial surfaces
With appropriately selected optical frequencies, pulses of radiation propagating through a system of chemically distinct and organized components can produce areas of spatially selective excitation. This paper focuses on a system in which there are two absorptive components, each one represented by surface adsorbates arrayed on a pair of juxtaposed interfaces. The adsorbates are chosen to be chemically distinct from the material of the underlying surface. On promotion of any adsorbate molecule to an electronic excited state, its local electronic environment is duly modified, and its London interaction with nearest neighbor molecules becomes accommodated to the new potential energy landscape. If the absorbed energy then transfers to a neighboring adsorbate of another species, so that the latter acquires the excitation, the local electronic environment changes and compensating motion can be expected to occur. Physically, this is achieved through a mechanism of photon absorption and emission by molecular pairs, and by the engagement of resonance transfer of energy between them. This paper presents a detailed analysis of the possibility of optically effecting such modifications to the London force between neutral adsorbates, based on quantum electrodynamics (QED). Thus, a precise link is established between the transfer of excitation and ensuing mechanical effects
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