Three separate teams have found analogues of Weyl fermions: massless elementary particles that were first predicted in 1929 but have never been observed.

Physicists searching for these fermions look for their unusual properties in the collective behaviour of other particles. Hong Ding and Tian Qian at the Chinese Academy of Sciences in Beijing and their colleagues saw these 'quasiparticles' by probing a sample of tantalum arsenide with a beam of X-rays. In July, a separate group of researchers led by Zahid Hasan at Princeton University in New Jersey announced that they had seen the particles in the same material. Ling Lu at the Massachusetts Institute of Technology in Cambridge and his colleagues reported seeing signs of the particles in the behaviour of light passing through a crystal.

Such experimental systems could allow researchers to probe the exotic properties associated with Weyl particles.

Phys. Rev. X 5, 031013 (2015) ; Science 349, 613–617 ; 622–624 (2015) ;