Topological Semimetals: How to find them
In this talk, I will introduce the family of topological semimetals (TSM) including Dirac semimetal (DSM), Weyl semimetal (WSM), and triply degenerate nodal point semimetal (TPSM). In ideal case, they have and only have nodal points at the Fermi level, but they are classified according to the distribution and degeneracy of these nodal points. The quasiparticles of low energy excitation in DSM and WSM can be described by massless Dirac and Weyl equation, respectively, while those in TPSM have no counterpart in the high-energy field theory. To find realistic materials hosting these exotic topological quantum states is very challenge and crucial to the further experimental studies. We noticed that the unusual temperature dependent diamagnetism is a strong hint of existence of linear Dirac cone like bands around Fermi level. This has been confirmed in DSMs Na3Bi and HfTe5 at phase transition. It also leads to the success in locating TaAs, the first available WSM. The experimental studies of these materials have stimulated many research works, including the characteristic chiral anomaly and Fermi arcs. Finally, the TSM family members and their relationship with each other are summarized.[Introduction of the lecturer] Professor Hongming Weng predicted based on the theoretical band analysis that materials in the TaSe family can be described as a Weyl semimetal and proved the prediction in a collaboration with experimental groups. For this mile-stone achievement,
Professor Weng will receive the Nishina Asia award this year. For the reception of the award he will visit Japan and kindly give a seminar at ISSP. We hope everybody join and listen to his lectures on the exotic materials.