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UID:UW-Physics-Event-2040
DTSTART:20110412T150000Z
DURATION:PT1H0M0S
DTSTAMP:20260419T142824Z
LAST-MODIFIED:20110404T124729Z
LOCATION:5310 Chamberlin
SUMMARY:Interacting fermions on the honeycomb and its bilayer\, R. G. 
 Herb Condensed Matter Seminar\, Oskar Vafek\, Florida State University
DESCRIPTION:Electron-electron interaction effects on the graphene hone
 ycomb lattice\, and its AB stacked bilayer\, will be compared. While t
 here are no low temperature weak coupling instabilities of interacting
  massless Dirac fermions in 2D\,  such instabilities are unavoidable f
 or two parabolically touching bands. We use weak-coupling renormalizat
 ion group as well as strong-coupling expansion to determine the domina
 nt ordering tendency for spinless and spin 1/2 fermions on the bilayer
  for models with different microscopic interactions. We find that for 
 spinless fermions on the honeycomb bilayer the broken symmetry state i
 s typically a gapped insulator with either broken inversion or broken 
 time-reversal symmetry\, with a quantized anomalous Hall effect (i.e.\
 , either a layer polarized state or an anomalous quantum Hall state). 
 Additionally\, a tight-binding model with nearest-neighbor hopping and
  nearest-neighbor repulsion is studied in weak and strong couplings an
 d in each regime a gapped phase with inversion symmetry breaking is fo
 und. In the strong-coupling limit\, the ground-state wave function can
  be constructed for vanishing in-plane hopping but finite interplane h
 opping\, which explicitly displays the broken inversion symmetry and a
  finite difference between the number of particles on the two layers. 
 For spin-1/2 fermions the resulting instabilities are studied as a fun
 ction of the range of the electron-electron repulsion. For longer rang
 e interactions (several tens of lattice spacings) the dominant orderin
 g tendency is towards an electronic nematic\, while for short range re
 pulsion (of order a lattice spacing as in a repulsive Hubbard model) t
 he leading instability is found towards a Neel antiferromagnet.<br>
\n
 <br>
\n[1] Oskar Vafek and Kun Yang\, PRB 81\, 041401 (2010). (Physics
  3\, 1 (2010))<br>
\n[2] Oskar Vafek\, PRB 82\, 205106 (2010)
URL:https://www.physics.wisc.edu/events/?id=2040
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