Realization of Practical Eightfold Fermions and Fourfold van Hove Singularity in TaCo$_2$Te$_2$
cond-mat.str-el
/ Authors
Hongtao Rong, Zhenqiao Huang, Xin Zhang, Shiv Kumar, Fayuang Zhang, Chengcheng Zhang, Yuan Wang, Zhanyang Hao, Yongqing Cai, Le Wang
and 13 more authors
Cai Liu, Xiao-Ming Ma, Shu Guo, Bing Shen, Yi Liu, Shengtao Cui, Kenya Shimada, Quansheng Wu, Junhao Lin, Yugui Yao, Zhiwei Wang, Hu Xu, Chaoyu Chen
/ Abstract
Space groups describing the symmetry of lattice structure allow the emergence of fermionic quasiparticles with various degeneracy in the band structure. Theoretical efforts have predicted many materials hosting fermions with the highest degeneracy, i.e., eightfold fermions, yet lacking experimental realization. Here, we explore the band degeneracies in TaCo$_2$Te$_2$ crystals. Through systematic experimental and theoretical analyses, we establish TaCo$_2$Te$_2$ as a nonsymmorphic crystal with negligible spin-orbit coupling (SOC) and long-range magnetic order. These critical properties guarantee the first realization of practical eightfold fermions and fourfold van Hove singularity, as directly observed by photoemission spectroscopy. TaCo$_2$Te$_2$ serves as a topological quantum critical platform, which can be tuned into various magnetic, topologically trivial, and nontrivial phases by adding strain, magnetic field, or SOC. The latter is demonstrated by our first-principles calculations, which show that enhancing SOC in TaCo$_2$Te$_2$ will promote the experimental observation of bulk hourglass fermions. Our results establish TaCo$_2$Te$_2$ as a unique platform to explore states of matter intertwining magnetism, correlation, symmetry, and band topology.