## 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.
• 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.