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SUMMARY:The quest for electron-hole superfluidity - Prof David Nielson\, U
 niversity of Camerino\, Italy
DTSTART:20150422T130000Z
DTEND:20150422T140000Z
UID:TALK58844@talks.cam.ac.uk
CONTACT:Teri Bartlett
DESCRIPTION:Interacting electrons and holes in solids are predicted to for
 m a superfluid at high temperatures thanks to the Coulomb pairing which is
  very strong compared with the pairing interaction in conventional superco
 nductors. [1]  The electrons and holes must kept apart in two adjacent thi
 n conducting layers separated by a thin insulating barrier\, so they stron
 gly attract but cannot recombine.[2\,3\,4]\n  \nThere have been major expe
 rimental projects to realise this phenomenon in double quantum wells in se
 miconductor heterostructures of GaAs.[5\,6]  However\, these have led to r
 ather inconclusive results.  In this talk the issue of the optimal ranges 
 for the experimental parameters\, temperature\, well width\, well separati
 on\, will be discussed.\n\nAlso discussed will be the theoretical issue of
  the self-consistent treatment of the screening of the electron-hole pair 
 Coulomb interaction in the presence of a superfluid quantum condensate\,[7
 ] and the relative importance of screening in the weak-coupled BCS regime\
 , the cross-over regime and the Bose-Einstein condensation regime.\nFinall
 y\, the dependence of the phenomenon on dimensionality will be discussed\,
  contrasting the superfluid properties for two coupled two-dimensional qua
 ntum well sheets with the superfluid properties for two coupled quasi-one 
 dimensional wires.[8]\n\n[1] Room-temperature superfluidity in graphene bi
 layers\, Hongki Min\, Rafi Bistritzer\, Jung-Jung Su\, and A. H. MacDonald
 \, \, Physical Review B 78\, 121401(R) (2008).\n[2] Feasibility of superfl
 uidity of paired spatially separated electrons and holes\; a new supercond
 uctivity mechanism\, Yu. E. Lozovik and V.I. Yudson\, JETP Letters 22\, 27
 4 (1975).\n[3] Effects of density imbalance on the BCS-BEC crossover in se
 miconductor electron-hole bilayers\, P. Pieri\, D. Neilson\, and G.C. Stri
 nati\, Physical Review B 75\, 113301 (2007).\n[4] High-Temperature Superfl
 uidity in Double-Bilayer Graphene\, A. Perali\, D. Neilson\, and A. R. Ham
 ilton\, Physical Review Letters 110\, 146803 (2013).\n[5] Anomalous Coulom
 b Drag in Electron-Hole Bilayers\, A. F. Croxall\, K. Das Gupta\, C. A. Ni
 coll\, M. Thangaraj\, H. E. Beere\, I. Farrer\, D. A. Ritchie\, and M. Pep
 per\, Physical Review Letters 101\, 246801 (2008).\n[6] Coulomb Drag in th
 e Exciton Regime in Electron-Hole Bilayers\, J. A. Seamons\, C. P. Morath\
 , J. L. Reno\, and M. P. Lilly\, Physical Review Letters 102\, 026804 (200
 9).\n[7] Excitonic superfluidity and screening in electron-hole bilayer sy
 stems\, D. Neilson\, A. Perali\, and A. R. Hamilton\, Physical Review B 89
 \, 060502(R) (2014).\n[8]The gap amplification at a shape resonance in sup
 erlattice of quantum stripes: mechanism for high-Tc\, A. Perali\, A. Bianc
 oni\, A. Lanzara\, and N.L. Saini\, Solid State Communications 100\, 186 (
 1996).\n
LOCATION:Mott Seminar Room (Mott Building Room 531)\, Cavendish Laboratory
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