Weyl points in condensed matter are analogous to magnetic monopoles in momentum space. Constrained by the Nielsen-Ninomiya no-go theorem, it is well believed that Weyl points should appear in pairs with opposite charges. As a consequence, Fermi arcs occur on surfaces which connect the projections of the WPs with opposite chiral charges. Paired Weyl points and related surface Fermi arcs are two essential characters to search for Weyl semimetal in all provious studies. However, this situation can be circumvented. Here, the authors report one unpaired Weyl point without surface Fermi arc for the first time, which is surrounded by charged Weyl nodal walls in PtGa. The attendance of closed Weyl nodal walls allow unpaired Weyl points to accour inside it.
Meanwhile, the geometry between unpaired WPs and Weyl nodal walls is quite different from that of all previous Weyl semimetals, so that the transport properties are expected to change significantly in this new kind of WSMs, which needs further study in the future. The observation will open a new avenue to the bulk topological properties of Weyl fermions in solids, which will promote the understanding of basic topological physics, and application of WSMs into spintronics.
Read more at Nature Communications:
https://www.nature.com/articles/s41467-021-24289-0
28 Jun 2021