Falko Pientka

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In the first part of the talk, I will propose a transport experiment of
excitons in 2d transition-metal dichalcogenides. Due to their
interactions with unbound electrons in the Fermi sea, excitons are
dressed by a cloud of particle-hole excitations forming Fermi polarons.
An in-plane electric field cannot directly accelerate neutral excitons,
however, due to the polaronic dressing, the unbound electrons will drag
the excitons along. This phenomenon is similar to Coulomb drag in
bilayer semiconductors. We determine the drag conductivity for a low
density of excitons using simple arguments as well as a diagrammatic
calculation based on a self-consistent T matrix approximation. Due to
the strong nonperturbative coupling, the exciton drag mobility is
expected to be of the same order as the electron mobility even at zero
temperature.
Time permitting, I will discuss a novel probe of quantum Hall
ferromagnetism in graphene based on thermal transport in the second part
of the talk. Strong interactions lift the high degeneracy of the
zero-energy Landau level in graphene mono- and bilayers, giving rise to
a rich phase diagram of competing spin and valley order. Here we show
that thermal transport at low temperatures can give compelling evidence
for spontaneous symmetry breaking and exhibits many other signatures
distinguishing the various phases.

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Harvard University
Seminar Room 0.03, ETP
Contact: not specified