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.

【講師紹介】
Weng先生は、新しいトポロジカル状態として知られるワイル半金属状態がTaAs系物質において実現されることを第一原理計算に基づいて予言し、さらに、実験グループとの共同研究により初めて実証したことで知られる気鋭の若手研究者です。この度、これらの研究成果に対して仁科アジア賞が授与されることとなり、来日されることから、物性研での談話会をお願いすることといたしました。
最近の話題のテーマであるワイル半金属について理解を深める良い機会ですので、　是非、皆様ご参加ください。