Observation of Weyl nodes in TaAs

Understand

In 1929, H.

• Weyl proposed that the massless solution of Dirac equation represents a pair of new type particles, the so-called Weyl fermions [1].
• However the existence of them in particle physics remains elusive for more than eight decades.
• Recently, significant advances in both topological insulators and topological semimetals have provided an alternative way to realize Weyl fermions in condensed matter as an emergent phenomenon: when two non-degenerate bands in the three-dimensional momentum space cross in the vicinity of Fermi energy (called as Weyl nodes), the low energy excitation behaves exactly the same as Weyl fermions.