Wednesday, September 25, 2013

DOE ECMP PI meeting, day 2 - things I learned

Very brief list of things I learned about during day 2 yesterday:
  • Due to optical nonlinearities, it is possible to get broadband negative (left-handed, that is) refraction from (18 layer thick) graphene.
  • In a strong perpendicular-to-plane magnetic field, you can detect (optically) evidence of 1-d subband formation and e-e interactions.
  • The optical properties of graphene are very very rich.  That is, complicated.
  • Doug Hofstadter was right.
  • With an in-plane magnetic field, you can see physics that looks like the quantum spin Hall effect in single-layer graphene.
  • Trying to tune the bandgap of GaAs down to 1 V via nitrogen doping without killing the mobility is very hard.
  • Ballistic phonon pulses are a very cool way of detecting defects and interface roughness basically with sonar!
  • You can measure the exchange field between a magnet and electrons in a superconductor if you can work with ultrathin films (field in plane).
  • There are still some weird issues associated with electronic decoherence in the mesoscopic world - coherence times seem to saturate at the lowest temperatures in various etched semiconductor and bismuth nanowires.
  • Pumping spin currents via the spin Hall effect is still cool.
  • Electronic heating above the lattice temperature in graphene is more complicated than it would appear.
  • Anisotropy in the electronic structure at B=0 leads to modified anisotropy in composite fermions at \( \nu = 1/2 \).
  • The \( \nu = 5/2 \) quantum Hall state is surprisingly robust as mobility goes down.  That means that short-range, high-angle scattering doesn't really kill the state, which is good, and that mobility as our favorite proxy for sample quality is a poor guide in this regime, which is interesting.
  • My colleague Rui-Rui Du has a really great and exciting system for looking at topological edge states and quantum spin Hall in InAs/GaSb quantum well structures available from a commercial vendor.

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