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PRODID:UW-Madison-Physics-Events
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SEQUENCE:0
UID:UW-Physics-Event-2291
DTSTART:20111118T213000Z
DURATION:PT1H0M0S
DTSTAMP:20260420T132552Z
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.<br>
\n<br>
\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.<br>
\n
URL:https://www.physics.wisc.edu/events/?id=2291
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