Discovery of a maximally charged Weyl point

• Main Authors: Chen, Qiaolu, Chen, Fujia, Pan, Yuang, Cui, Chaoxi, Yan, Qinghui, Zhang, Li, Gao, Zhen, Yang, Shengyuan A., Yu, Zhi-Ming, Chen, Hongsheng, Zhang, Baile, Yang, Yihao
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2023
• Subjects: Science::Physics; Crystal Structure; Hypothesis Testing
• Online Access: https://hdl.handle.net/10356/166236
• Institution: Nanyang Technological University

The hypothetical Weyl particles in high-energy physics have been discovered in three-dimensional crystals as collective quasiparticle excitations near two-fold degenerate Weyl points. Such momentum-space Weyl particles carry quantised chiral charges, which can be measured by counting the number of Fermi arcs emanating from the corresponding Weyl points. It is known that merging unit-charged Weyl particles can create new ones with more charges. However, only very recently has it been realised that there is an upper limit - the maximal charge number that a two-fold Weyl point can host is four - achievable only in crystals without spin-orbit coupling. Here, we report the experimental realisation of such a maximally charged Weyl point in a three-dimensional photonic crystal. The four charges support quadruple-helicoid Fermi arcs, forming an unprecedented topology of two non-contractible loops in the surface Brillouin zone. The helicoid Fermi arcs also exhibit the long-pursued type-II van Hove singularities that can reside at arbitrary momenta. This discovery reveals a type of maximally charged Weyl particles beyond conventional topological particles in crystals.