Quantum phase transitions and quantum criticality in two-dimensional helium

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• John Saunders*, Royal Holloway University of London
• Wednesday 07 November 2007, 11:15-12:15
• Mott Seminar Room, Cavendish Laboratory, Department of Physics.

If you have a question about this talk, please contact Robert Smith.

Two dimensional helium films provide simple model systems for the investigation of quantum phase transitions in two dimensions. Monolayer 3He absorbed on graphite, with various pre-platings, behaves as a two dimensional Mott-Hubbard system, complete with a density driven “metal-insulator” transition [1, 2]. In two dimensions the corrections to the temperature dependence of the heat capacity, beyond the term linear in T, are anomalous and attributed to quasi-1D scattering [3]. Bi-layer 3He films adsorbed on the surface of graphite show evidence of heavy fermion behaviour and quantum criticality [4, 5]. Here the metal insulator transition 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 “Kondo breakdown selective Mott transition” has recently been suggested [6]. On the other hand 4He films adsorbed on graphite allow the study of the superfluid-insulator transition [7], related to the superfluid-Mott insulator transition observed in cold atoms [8]. In the present case the transition 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.

• In collaboration with: A Casey, M Neumann, J Nyeki, J Parpia, B Cowan.

[1] Evidence for a Mott-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) [2] D Tsuji et al. J. Low Temp. Phys. 134, 31 (2004) [3] A V Chubukov et al. Phys. Rev. B71 , 205112 (2005) [4] Bilayer 3He; a simple two dimensional heavy fermion system with quantum criticality, Michael Neumann, Jan Nyeki, Brian Cowan, John Saunders. Science 317, 1356 (2007) [5] Heavy fermions in the original Fermi liquid. Christopher A Hooley and Andrew P Mackenzie. Science 317, 1332 (2007) [6] C Pepin, Phys. Rev. Lett. 98, 206401 (2007) and A Benlagra and C Pepin, arXiv: 0709.0354 [7] M P A Fisher et al. Phys. Rev. B40 , 546 (1989) [8] M Greiner et al. Nature 415, 39 (2002)

This talk is part of the Quantum Matter Seminar series.

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