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SUMMARY:Low temperature transport in an  electron-hole bilayer:  search fo
 r  excitonic phases and collective modes. - Kanti Das Gupta\, SP group\, C
 avendish Laboratory
DTSTART:20091111T111500Z
DTEND:20091111T121500Z
UID:TALK20955@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:Recently it has been possible to design  independently contact
 ed electron-hole bilayers (EHBL) with densities < 5e10/cm^2 and a separati
 on of 10-20 nm in a GaAs/AlGaAs system. Simple estimates show that in  the
 se EHBLs the interlayer interaction is stronger than the intralayer intera
 ctions. Excitonic superfluidity in\nsuch EHBLs with a spatially separated 
 layer of electrons and holes was first predicted  almost forty\nyears ago.
  Since then theoretical works have indicated the possibility of a very ric
 h phase diagram\, consisting of superfluid phases\, charge density waves\,
  Wigner crystals and a BCS-BEC crossover. However this system is enormousl
 y difficult to fabricate in practice. Only in last 2-3 years reliable meth
 ods to\nfabricate such devices have been found. Very recent experiments ha
 ve revealed novel features in the interlayer scattering (Coulomb drag) bel
 ow ~1K. The coulomb drag shows strong non-monotonic deviations from\na ~T^
 2 behaviour expected for Fermi-liquids at low temperatures. In addition\, 
 experimental data available so far indicate that the system somehow violat
 es Onsager's reciprocity theorem for four terminal measurement of resistan
 ces. Simultaneously an unexpected insulating behaviour in the single layer
  resistances (at a highly "metallic" regime with k_{F}l > 500) also appear
 s in both layers inspite of electron mobilities above 1e6cm^2/Vs and hole 
 mobilities above 1e5cm^2/Vs. The experimental results may indicate a compe
 tition between an excitonic ground state and a density modulated phase.\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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