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SUMMARY:Quantum phase transitions and quantum criticality in two-dimension
 al helium - John Saunders*\, Royal Holloway University of London
DTSTART:20071107T111500Z
DTEND:20071107T121500Z
UID:TALK8496@talks.cam.ac.uk
CONTACT:Robert Smith
DESCRIPTION:Two dimensional helium films provide simple model systems for 
 the investigation of quantum phase transitions in two dimensions. \n	Monol
 ayer 3He absorbed on graphite\, with various pre-platings\, behaves as a t
 wo dimensional Mott-Hubbard system\, complete with a density driven "metal
 -insulator" transition [1\, 2]. In two dimensions the corrections to the t
 emperature dependence of the heat capacity\, beyond the term linear in T\,
  are anomalous and attributed to quasi-1D scattering [3].\n	Bi-layer 3He f
 ilms adsorbed on the surface of graphite show evidence of heavy fermion be
 haviour and quantum criticality [4\, 5]. Here the metal insulator transiti
 on appears to arise from tuning both the bandwidth of the lower layer and 
 the Kondo coupling between layers. A theoretical model in terms of a “Ko
 ndo breakdown selective Mott transition” has recently been suggested [6]
 .\n	On the other hand 4He films adsorbed on graphite allow the study of th
 e superfluid-insulator transition [7]\, related to the superfluid-Mott ins
 ulator transition observed in cold atoms [8]. In the present case the tran
 sition is between a Kosterlitz-Thouless 2D superfluid and a (possibly hole
 -doped) Mott insulator. Both “density driven” and “bandwidth driven
 ” transitions are experimentally accessible. Here the superfluid density
  is being studied using torsional oscillator techniques\; the possibility 
 of a 2D supersolid phase will be discussed.\n\n* In collaboration with: A 
 Casey\, M Neumann\, J Nyeki\, J Parpia\, B Cowan.\n\n[1] Evidence for a Mo
 tt-Hubbard Transition in a Two-Dimensional 3He Fluid Monolayer\, A. Casey\
 , H. Patel\, J. Nyéki\, B. P. Cowan\, and J. Saunders Phys. Rev. Lett. 90
 \, 115301 (2003)\n[2] D Tsuji et al. J. Low Temp. Phys. 134\, 31 (2004)\n[
 3] A V Chubukov et al. Phys. Rev. B71\, 205112 (2005)\n[4] Bilayer 3He\; a
  simple two dimensional heavy fermion system with quantum criticality\, Mi
 chael Neumann\, Jan Nyeki\, Brian Cowan\, John Saunders. Science 317\, 135
 6 (2007)\n[5] Heavy fermions in the original Fermi liquid. Christopher A H
 ooley and Andrew P Mackenzie. Science 317\, 1332 (2007)\n[6] C Pepin\, Phy
 s. Rev. Lett. 98\, 206401 (2007) and A Benlagra and C Pepin\, \narXiv: 070
 9.0354\n[7] M P A Fisher et al. Phys. Rev. B40\, 546 (1989)\n[8] M Greiner
  et al. Nature 415\, 39 (2002)\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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