Eightfold fermionic excitation in a charge density wave compound
Xi Zhang, Qiangqiang Gu, Haigen Sun, Tianchuang Luo, Yanzhao Liu, Yueyuan Chen, Zhibin Shao, Zongyuan Zhang, Shaojian Li, Yuanwei Sun, Yuehui Li, Xiaokang Li, Shangjie Xue, Jun Ge, Ying Xing, Riccardo Comin, Zengwei Zhu, Peng Gao, Binghai Yan, Ji Feng, Minghu Pan, Jian Wang
Abstract
The 230 space group symmetries of three-dimensional crystal lattices permit the existence of quasiparticle excitations beyond the standard model of high-energy physics. Here, the authors propose that the TaTe${}_{4}$ crystal, with a quasi-one-dimensional lattice structure, holds an eightfold degenerate double Dirac point and a fourfold degenerate Dirac point in the charge density wave (CDW) ground state. The calculated band structure is consistent with Shubnikov--de Haas oscillation measurements. Further, an atomic step edge state is detected, suggesting nontrivial topology. This work reveals the CDW-induced topological phases and provides new insight into the interplay between the CDW and fermionic excitations.