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UID:UW-Physics-Event-2291
DTSTART:20111118T213000Z
DURATION:PT1H0M0S
DTSTAMP:20240319T084420Z
LAST-MODIFIED:20111013T124929Z
LOCATION:2241 Chamberlin Hall (coffee at 4:30 pm)
SUMMARY:Condensation of excitons and polaritons\, Physics Department C
olloquium\, Peter Littlewood\, Argonne National Laboratory
DESCRIPTION:Macroscopic phase coherence is one of the most remarkable
manifestations of quantum mechanics\, yet it seems to be the inevitabl
e ground state of interacting many-body systems. In the last two decad
es\, the familiar examples of superfluid He and conventional supercond
uctors have been joined by exotic and high temperature superconductors
\, ultra-cold atomic gases\, both bosonic and fermionic\, and recently
systems of excitons\, magnons\, and exciton-photon superpositions cal
led polaritons\, the subject of this talk.
\n
\nAn exciton is
the solid-state analogue of positronium\, made up of an electron and a
hole in a semiconductor\, bound together by the Coulomb interaction.
The idea that a dense system of electrons and holes would be unstable
toward an excitonic (electrical) insulator is one of the key ideas und
erlying metal-insulator transition physics. The further possibility th
at an exciton fluid would be a Bose-Einstein condensate was raised ove
r 40 years ago\, and has been the subject of an extensive experimental
search in a variety of condensed matter systems. Such a condensate wo
uld naturally exhibit phase coherence. Lately\, some novel experiments
with planar optical microcavities make use of the mixing of excitons
with photons to create a composite boson called a polariton that has a
very light mass\, and is thus a good candidate for a high-temperature
Bose condensate. Good evidence for spontaneous coherence has now been
obtained\, though there are special issues to resolve considering the
effects of low dimensionality\, disorder\, strong interactions\, and
especially strong decoherence associated with decay of the condensate
into environmental photons---since the condensate is a special kind of
laser.
\n
URL:https://www.physics.wisc.edu/events/?id=2291
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