Weyl Fermions

I came across this article and thought I would pass it along. It's a great breakthrough, with powerful implications for computing.

Weyl fermions are spotted at long last

Evidence for the existence of particles called Weyl fermions in two very different solid materials has been found by three independent groups of physicists. First predicted in 1929, Weyl fermions also have unique properties that could make them useful for creating high-speed electronic circuits and quantum computers. In 1928 Paul Dirac derived his eponymous equation, which describes the physics of spin-1/2 fundamental particles called fermions. For particles with charge and mass, he found that the Dirac equation predicts the existence of the electron and its antiparticle the positron, the latter being discovered in 1932.

However, there are other solutions of the Dirac equation that suggest the existence of more exotic particles than the familiar electron. In 1937 Ettore Majorana discovered a solution of the equation that describes a neutral particle that is its own antiparticle: the Majorana fermion. Although there is no evidence that Majorana fermions exist as fundamental particles, Majorana-like collective excitations (or quasiparticles) have been detected in condensed-matter systems. Another solution of the Dirac equation - this time for massless particles - was derived in 1929 by the German mathematician Hermann Weyl. For some time it was thought that neutrinos were Weyl fermions, but now it looks almost certain that neutrinos have mass and are therefore not Weyl particles.

Now, a group headed by Zahid Hasan at Princeton University has found evidence that Weyl fermions exist as quasiparticles - collective excitations of electrons - in the semimetal tanatalum arsenide (TaAs). In 2014 Hasan and colleagues published calculations that suggested that TaAs is "Weyl semimetal". This means that TaAs should have Weyl fermions in its bulk and a distinct feature on its surface called a "Fermi arc". Using a standard technique called angle-resolved photoemission spectroscopy (ARPES), the team found evidence of a Fermi arc. The team then used a technique called soft X-ray ARPES to probe deeper into the bulk of the material, where it found further evidence for Weyl fermions in the form of "Weyl cones" and "Weyl nodes" - both of which were in agreement with the researchers previous calculations.

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