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SUMMARY:Paradigms of the interaction effects in Fermi surface topological 
 reconstruction - Dr Joseph Betouras\, Loughborough University
DTSTART:20140313T141500Z
DTEND:20140313T151500Z
UID:TALK49104@talks.cam.ac.uk
CONTACT:Gareth Conduit
DESCRIPTION:Recently\, the theory of topological Lifshitz transition has b
 ecome the focus of much attention in complex materials such as high-Tc sup
 erconductors\, heavy fermions compounds etc. In this talk\, after reviewin
 g the basic concepts\, I will present two cases of topological Lifshitz tr
 ansitions involving (i)dipolar fermions in optical lattices and (ii) itine
 rant electrons close to a ferromagnetic quantum critical point but in the 
 disordered side.\n\nIn the first case\, we consider an experimentally real
 izable two dimensional model of non-interacting chains of spinless fermion
 s weakly coupled via a small inter-chain hopping with a repulsive inter-ch
 ain interaction. The phase diagram of this model has a surprising feature:
  an abrupt change in the Fermi surface as the interaction is increased. We
  study in detail this meta-nematic transition\, and show that the well-kno
 wn continuous Lifshitz transition is the critical endpoint of this first o
 rder quantum phase transition. Furthermore\, in the vicinity of the endpoi
 nt\, the order parameter has a non-perturbative BCS-like form. In the seco
 nd case\, the motivation for the work is provided by recent experiments on
  the material NaxCoO2. We particularly examine the role of paramagnetic fl
 uctuations in the development of an additional Fermi surface.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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