Tuesday, January 23, 2018

Weyl and Quasiparticles

Jim and Randy discuss quasiparticles recently found in condensed matter systems that mirror particles theorized nearly a hundred years ago, but never found in the vacuum. Weyl particles are massless fermions, and once it was hoped that neutrinos would turn out to be this kind of particle, and Majorana fermions have real-valued wave functions and therefore many strange and possibly useful properties.



1. The papers we read for this program:
  • Pal, P.B., "Dirac, Majorana, and Weyl Fermions." Am. J. Phys. 79, 485 (2011).
  • Mourik, Zuo, Frolov, Plissard, Bakkers, and Kouwenhoven, "Signatures of Majorana Fermions in Hybrid Superconductor-Semiconductor Nanowire Devices."  Science 336, 1003 (2012). [arXiv]
  • Nadj-Perge, Drozdov, Li, Chen, Jeon, Seo, MacDonald, Bernevig, and Yazsdani, "Observation of Majorana Fermions in Ferromagnetic Atomic Chains of a Superconductor." Science 346, 602 (2014) [arXiv]
  • Xu, et al., "Discovery of a Weyl Fermion State with Fermi Arcs in Niobium Arsenide." Nat. Phys.  11, 748 (2015) [arXiv]
  • Zhang, et al, Signatures of the Adler-Bell-Jackiw Chiral Anomaly in a Weyl Fermion Semimetal." Nat. Comm. 10735 (2016) [arXiv]
2.  Popular papers we may have read:
  • Wilczek, F., "Why are there Analogies between Condensed Matter and Particle Theory?" Physics Today, January 1998, 11.
  • Wilczek, F., "Majorana Returns." Nature Physics 5, 614 (2009)
  • Balents, Leon, "Weyl Electrons Kiss." Physics 4, 36 (2011).
  • "After a Weyl" Nat. Phys.  11, 697 (2015)
  • Bernevig, B.A., "Weyl Electrons Kiss." Nat. Phys. 11, 699 (2015)
3. Original Papers:
  • Weyl, H., "Gravitation and the Electron." ..., 323 (1929).
  • Majorana, "A Symmetric Theory of Electrons and Positrons." Il Nuovo Cimento, 14, 171 (1937).
4. I was wrong.  "Weyl" rhymes with "pile," not with "pail."

5. Our subreddit.

Monday, January 22, 2018


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Wednesday, January 10, 2018

The Origin of Inertia

Randy tells Jim about a scheme that uses Mach's Principle - the idea that there is a preferred background frame with respect to the fixed stars - to explain the origin of inertia. Why exactly does an object in motion stay in motion?



1. The papers we read for this program:

2. In addition, Randy sent me a lot of blog and other forum posts for background:

3. Our discussion on Gravitoelectromagnetism..

4. Our discussion of Aharonov and Rohrlich's Quantum Paradoxes, nine of the ten recorded episodes. I don't think we get into the retrocausal part of it.

5. Our subreddit.