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. 

Application of Advanced Scanning Probe Microscopies in Biophysics and Condensed Matter Physics: from Neuronal Networks to Reduced Graphene Oxide Nanosensors

Invented in 1986, the Atomic Force Microscope (AFM) is probably the single most important tool in nanotechnology. A whole host of AFM-based techniques called Scanning Probe Microscopies (SPMs) have been developed to study a wide range of systems from imaging surfaces with sub-nanometer (sometimes even atomic) resolution and manipulation of matter at the level of molecules (nanoscale level) to studies of physical properties of biomolecules such as proteins and nucleic acids. In this presentation I will exemplify the use of SPMs to study some fundamental biophysical processes as well as the electronic transport in low-dimensional systems. As a first example, I will show that the AFM can be used to immobilize proteins at well-defined locations directly onto gold substrates, and to control effectively the adhesion, growth and interconnectivity of cortical neurons on these surfaces. I will demonstratethat this method allows us to control geometric and chemical factors that can be used to influence the growth and development of neuronal assemblages in simple geometries. As a second example, I will describe the use of SPM to study the doping mechanism and the charge transport in reduced graphene oxide chemical sensors.

Condensed Matter Seminar Calendar

Once Upon a Time in Kamchatka: The Extraordinary Search for Natural Quasicrystals

Refreshments at 3pm in CP179.

https://pa.as.uky.edu/van-winter-memorial-lecture-0

Surprising trace anomaly from freakolography 

Yu Nakayama

(Caltech)

Mon. Mar. 19 @ 12:00 PM

Room CP 179