Chiral Dirac Fermion in a Collinear Antiferromagnet
Ao 奥 Zhang 张, Ke Deng, Jieming 洁明 Sheng 盛, Pengfei 鹏飞 Liu 刘, Shiv Kumar, K. Shimada, Zhicheng 志诚 Jiang 江, Zhengtai 正太 Liu 刘, Dawei Shen, Jiayu 嘉裕 Li 李, Jun 俊 Ren 任, Tao Wang, Liang 良 Zhou 周, Yoshihisa Ishikawa, Takashi Ohhara, Qiang Zhang, Garry J. McIntyre, Dehong Yu, Enke Liu, Liusuo 留锁 Wu 吴, Chaoyu 朝宇 Chen 陈, Qihang 奇航 Liu 刘
Abstract
In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it is predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral “Dirac-like” fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Such an unconventional chiral fermion, protected by a hidden SU (2) symmetry in the hierarchy of an enhanced crystallographic group, namely spin space group, is not experimentally verified yet. Here, by angle-resolved photoemission spectroscopy measurements, we reveal the surface origin of the electron pocket at the Fermi surface in collinear antiferromagnet CoNb 3 S 6 . Combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions. Our work provides spectral evidence of the chiral Dirac-like fermion caused by particular spin symmetry in CoNb 3 S 6 , paving an avenue for exploring new emergent phenomena in antiferromagnets with unconventional quasiparticle excitations.