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UID:UW-Physics-Event-2040
DTSTART:20110412T150000Z
DURATION:PT1H0M0S
DTSTAMP:20240328T184437Z
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.
\n
\n[1] Oskar Vafek and Kun Yang\, PRB 81\, 041401 (2010). (Physics
3\, 1 (2010))
\n[2] Oskar Vafek\, PRB 82\, 205106 (2010)
URL:https://www.physics.wisc.edu/events/?id=2040
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