Friday, March 19, 2021

APS March Meeting, Day 4

 Yesterday was also very chaotic, and so I have had to make a reminder to watch some talks later.  Very briefly:

  • Burkard Hillebrands gave a talk about creating room temperature Bose Einstein condensates out of magnons.  When first hearing about this a few years ago I wondered how this worked, since magnons are not strictly conserved.  They do have a minimum energy to be created, however, and if losses (to phonons) are sufficiently weak, then with the right population manipulation (either by rapid cooling or parametric pumping) you can create a BEC, in the same way that one can get a BEC from ultracold atoms in a somewhat leaky trap.  He showed evidence of a magnon condensate Josephson junction with the ac Josephson effect.  Neat stuff.  A magnonics roadmap has also just come out, for those interested in applications.
  • There was a nice contributed talk by Ruofan Li from the Ralph group at Cornell, looking at magnon transport in films of the magnetic insulator MgAl2O4.  The found an anisotropy in the magnon diffusion length that correlates with the magnetic anisotropy of the material along crystallographic directions.
  • Andrea Cavalleri spoke about his work on light-induced superconducting-like response in various materials, particularly K3C60.  His group has a recent result showing that they can trigger an apparently superconducting state (based on the conductivity) that is metastable for tens of nanoseconds at temperatures far above the equilibrium superconducting transition.  
  • A large part of my afternoon was spent at this session about pairing in the high-Tc normal state.  My fellow speakers gave uniformly excellent talks, and according to the session chair the turnout was actually pretty good.  As a proponent of noise measurements as interesting probes, I was very impressed by the recent results from Milan Allan, whose group has combined noise measurements with STM, and revealed clear evidence of pairing well above the bulk Tc in TiN.
There are multiple other talks that I want to watch later on as well, if I can find the time.

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