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Condensed Matter Seminar: Babak Seredjeh

Date:
-
Location:
179 Chem-Phys Bldg

Topological Exciton Condensate



Babak Seradjeh (IU)


Recent advances in the study of band insulators have revealed the
existence of new topological invariants that characterize these
materials. Among the three-dimensional time-reversal invariant
insulators a "strong" topological insulator (STI) was predicted to
exist, shortly followed by experimental confirmations in several
Bi-related materials with strong spin-orbit interaction. The STI is
physically distinguished by surface states with an odd number of Fermi
level crossing pairs, which remain metallic in the presence of weak
disorder. These states exhibit linear dispersion and behave as
massless Dirac fermions familiar from the physics of graphene. Having
an odd number of Dirac fermions leads to some exotic properties
associated with surfaces of a STI, such as a fractional quantum Hall
conductivity.

We have recently predicted that a "topological exciton condensate" is
spontaneously formed by the Coulomb interaction in a thin-film STI,
which intriguingly supports vortices with a precisely fractional value
of charge, e/2. This is a distinct correlated phase of matter enabled
by the special properties of topological insulators. I shall review
these developments and present our theory of the topological exciton
condensate. I will also discuss recent results on the effects of
particle-hole imbalance which show a spatially modulated condensate
can form in this case akin to the elusive
Fulde-Ferrel-Larkin-Ovchinikov state in an s-wave superconductor. I
will conclude by suggestions for the experimental observation of this
novel condensate.

 

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This week's CM/CAM seminar will be given by Babak Seradjeh, a new professor at Indiana University-Bloomington. His will speak about his work onthin films of topological insulators, but there are are also interesting connections with graphene.

Dont miss it! Refreshments will be provided before.