Weyl Fermions...

The surface of the double-gyroid photonic crystal used by Marin Soljačić and colleagues. A US dime is shown for scale. (Courtesy: Ling Lu)

Topics: Consumer Electronics, Particle Physics, Photonics, Quantum Computer, Theoretical Physics

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).

Physics World: Weyl fermions are spotted at long last, Hamish Johnston