Friday, September 15, 2017

DOE experimental condensed matter physics PI meeting, day 3

And from the last half-day of the meeting:

  • Because the mobile electrons in graphene have an energy-momentum relationship similar to that of relativistic particles, the physics of electrons bound to atomic-scale defects in graphene has much in common with the physics that sets the limits on the stability of heavy atoms - when the kinetic energy of the electrons in the innermost orbitals is high enough that relativistic effects become very important.  It is possible to examine single defect sites with a scanning tunneling microscope and look at the energies of bound states, and see this kind of physics in 2d.  
  • There is a ton of activity concentrating on realizing Majorana fermions, expected to show up in the solid state when topologically interesting "edge states" are coupled to superconducting leads.  One way to do this would be to use the edge states of the quantum Hall effect, but usually the magnetic fields required to get in the quantum Hall regime don't play well with superconductivity.  Graphene can provide a way around this, with amorphous MoRe acting as very efficient superconducting contact material.  The results are some rather spectacular and complex superconducting devices (here and here).
  • With an excellent transmission electron microscope, it's possible to carve out atomically well defined holes in boron nitride monolayers, and then use those to create confined potential wells for carriers in graphene.  Words don't do justice to the fabrication process - it's amazing.  See here and here.
  • It's possible to induce and see big collective motions of a whole array of molecules on a surface that each act like little rotors.
  • In part due to the peculiar band structure of some topologically interesting materials, they can have truly remarkable nonlinear optical properties.
My apologies for not including everything - side discussions made it tough to take notes on everything, and the selection in these postings is set by that and not any judgment of excitement.  Likewise, the posters at the meeting were very informative, but I did not take notes on those.


Alex said...

Interesting stuff!

The papers linked to under the third bullet point seem to use STM manipulation, not TEM (but maybe I have missed something?).

Douglas Natelson said...

Hi. It's a multi step situation. They use TEM to make the holey hBN, and then after they transfer graphene to make the final structure, they image the electronic states of the graphene with STM.