17 research outputs found
Exciton condensates in semiconductor quantum wells emit coherent light
We show that a quasi-two dimensional condensate of optically active excitons
emits coherent light even in the absence of population inversion. This allows
an unambiguous and clear experimental detection of the condensed phase. We
prove that, due to the exciton-photon coupling, quantum and thermal
fluctuations do not destroy condensation at finite temperature. Suitable
conditions to achieve condensation are temperatures of a few K for typical
exciton densities, and the use of a pulsed, and preferably circularly
polarized, laser.Comment: 5 pages, no figure
Exchange and correlation as a functional of the local density of states
A functional is presented, in which the exchange
and correlation energy of an electron gas depends on the local density of
occupied states. A simple local parametrization scheme is proposed, entirely
from first principles, based on the decomposition of the exchange-correlation
hole in scattering states of different relative energies. In its practical
Kohn-Sham-like form, the single-electron orbitals become the independent
variables, and an explicit formula for the functional derivative is obtained.Comment: 5 pages. Expanded version. Will appear in Phys. Rev.
Deep inelastic neutron scattering on Pb-207 and NaHF2 as a test of detectors array on the VESUVIO spectrometer
A prototype array of resonance detectors for deep inelastic neutron
scattering experiments has been installed on the VESUVIO spectrometer,
at the ISIS spallation neutron source. Deep inelastic neutron scattering
measurements on a reference lead sample and on NaHF2 molecular system
are presented. Despite on an explorative level, the results obtained for
the values of mean kinetic energy < E-k > are found in good agreement
with the theoretical predictions, thus assessing the potential
capability of the device for a routine use on the instrument. (C) 2007
Elsevier B.V. All rights reserved