Wednesday, September 13, 2017

DOE experimental condensed matter PI meeting, day 2

More things I learned:

  • I've talked about skyrmions before.  It turns out that by coupling a ferromagnet to a strong spin-orbit coupling metal, one can stabilize skyrmions at room temperature.  They can be visualized using magnetic transmission x-ray microscopy - focused, circularly polarized x-ray studies.   The skyrmion motion can show its own form of the Hall effect.  Moreover, it is possible to create structures where skyrmions can be created one at a time on demand, and moved back and forth in a strip of that material - analogous to a racetrack memory.
  • Patterned arrays of little magnetic islands continue to be a playground for looking at analogs of complicated magnetic systems.  They're a kind of magnetic metamaterial.  See here.  It's possible to build in frustration, and to look at how topologically protected magnetic excitations (rather like skyrmions) stick around and can't relax.
  • Topological insulator materials, with their large spin-orbit effects and surface spin-momentum locking, can be used to pump spin and flip magnets.  However, the electronic structure of both the magnet and the TI are changed when one is deposited on the other, due in part to interfacial charge transfer.
  • There continues to be remarkable progress on the growth and understanding of complex oxide heterostructures and interfaces - too many examples and things to describe.
  • The use of nonlinear optics to reveal complicated internal symmetries (talked about here) continues to be very cool.
  • Antiferromagnetic layers can be surprisingly good at passing spin currents.  Also, I want to start working on yttrium iron garnet, so that I can use this at some point in a talk.
  • It's possible to do some impressive manipulation of the valley degree of freedom in 2d transition metal dichalcogenides, creating blobs of complete valley polarization, for example.  It's possible to use an electric field to break inversion symmetry in bilayers and turn some of these effects on and off electrically.
  • The halide perovskites actually can make fantastic nanocrystals in terms of optical properties and homogeneity.

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