The discovery of Weyl semimetal TaAs was highlighted as one of the Top Ten Breakthroughs in year 2015 by Physics World. The prediction of the nontrivial band topology in TaAs was made by Dr. Hsin Lin’s theory group using first-principles electronic structures calculations, followed by its experimental verification done by their collaborators in Princeton University. Since Hermann Weyl proposed Weyl equations in 1929, the Weyl fermion has not been observed in high energy/particle physics. The electronic band structures of crystalline TaAs can host quasiparticles obeying Weyl equations and are topologically nontrivial. The study of Weyl fermions has become a hot topic at the present forefront research.

Weyl fermions carry topological chiral charges and always appear in pairs of opposite chirality. Two Weyl fermions with opposite chirality are connected by Fermi arcs on the surface of crystals. The pairwise creation and annihilation of Weyl fermions usually involve a band inversion. On the other hand, crystal structures can also exhibit chirality. The mirror image of a chiral crystal cannot be superimposed on itself. The universal link between topological chiral charges and structural chirality is recently revealed by Dr. Hsin Lin’s group and collaborators in Nature Materials 17, 978, (2018). The article is also highlighted in Nature Materials news & views. (doi: 10.1038/s41563-018-0210-6)

1. Nature Materials, published on October 1, 2018 Topological quantum properties of chiral crystals

2. Nature volume 562, 91 (12 September 2018) Giant and anisotropic many-body spin–orbit tunability in a strongly correlated kagome magnet

3. Nature Communications volume 9, Article number: 4153 (2018) Quasiparticle interference and nonsymmorphic effect on a floating band surface state of ZrSiSe