42,470 research outputs found
Gap and pseudogap evolution within the charge-ordering scenario for superconducting cuprates
We describe the spectral properties of underdoped cuprates as resulting from
a momentum-dependent pseudogap in the normal state spectrum. Such a model
accounts, within a BCS approach, for the doping dependence of the critical
temperature and for the two-parameter leading-edge shift observed in the
cuprates. By introducing a phenomenological temperature dependence of the
pseudogap, which finds a natural interpretation within the stripe
quantum-critical-point scenario for high-T_c superconductors, we reproduce also
the T_c-T^* bifurcation near optimum doping. Finally, we briefly discuss the
different role of the gap and the pseudogap in determining the spectral and
thermodynamical properties of the model at low temperatures.Comment: 13 pages (EPY style), 7 enclosed figures, to appear on Eur. Phys. J.
Restrictions on the coherence of the ultrafast optical emission from an electron-hole pairs condensate
We report on the transfer of coherence from a quantum-well electron-hole
condensate to the light it emits. As a function of density, the coherence of
the electron-hole pair system evolves from being full for the low density
Bose-Einstein condensate to a chaotic behavior for a high density BCS-like
state. This degree of coherence is transfered to the light emitted in a damped
oscillatory way in the ultrafast regime. Additionally, the photon field
exhibits squeezing properties during the transfer time. We analyze the effect
of light frequency and separation between electron and hole layers on the
optical coherence. Our results suggest new type of ultrafast experiments for
detecting electron-hole pair condensation.Comment: 4 pages,3 figures, to be published in Physical Review Letters. Minor
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UMD Banach spaces and square functions associated with heat semigroups for Schr\"odinger and Laguerre operators
In this paper we define square functions (also called Littlewood-Paley-Stein
functions) associated with heat semigroups for Schr\"odinger and Laguerre
operators acting on functions which take values in UMD Banach spaces. We extend
classical (scalar) L^p-boundedness properties for the square functions to our
Banach valued setting by using \gamma-radonifying operators. We also prove that
these L^p-boundedness properties of the square functions actually characterize
the Banach spaces having the UMD property
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