## Tuesday, September 17, 2019

### DOE experimental condensed matter PI meeting, day 1

The first day of the DOE ECMP PI meeting was very full, including two poster sessions.  Here are a few fun items:

• Transition metal dichalcogenides (TMDs) can have very strongly bound excitons, and if two different TMDs are stacked, you can have interlayer excitons, where the electron and hole reside in different TMD layers, perhaps separated by a layer or two of insulating hBN.  Those interlayer excitons can have long lifetimes, undergo Bose condensation, and have interesting optical properties.  See here, for example.
• Heterojunctions of different TMDs can produce moire lattices even with zero relative twist, and the moire coupling between the layers can strongly affect the optical properties via the excitons.
• Propagating plasmons in graphene can have surprisingly high quality factors (~ 750), and combined with their strong confinement have interesting potential.
• You can add AlAs quantum wells to the list of materials systems in which it is possible to have very clean electronic transport and see fractional quantum Hall physics, which is a bit different because of the valley degeneracy in the AlAs conduction band (that can be tuned by strain).
• And you can toss in WSe2 in there, too - after building on this and improving material quality even further.
• There continues to be progress in trying to interface quantum Hall edge states with superconductors, with the end goal of possible topological quantum computing.  A key question is understanding how the edge states undergo Andreev processes at superconducting contacts.
• Application of pressure can take paired quantum Hall states (like those at $\nu = 5/2, 7/2$) and turn them into unpaired nematic states, a kind of quantum phase transition.
• With clever (and rather involved) designs, it is possible to make high quality interferometers for fractional quantum Hall edge states, setting the stage for detailed studies of exotic anyons.

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