Discovery of Dirac nodal line in non-symmorphic semimetal Nb₃SiTe₆
Ro-Ya Liu1,2,3,5*, Angus Huang4, Raman Sankar2, Shih-Chang Weng5, Meng-Kai Lin1,6, Peng Chen7, Joseph Andrew Hlevyack1, Alexei Fedorov3, Cheng-Maw Cheng5, Jonathan Denlinger3, Chia-Seng Chang2, Horng-Tay Jeng4, Tien-Ming Chuang2, Tai-Chang Chiang1
1Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
2Institute of Physics, Academia Sinica, Taipei, Taiwan
3Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
4Department of Physics, National Tsing Hua University, Hinchu, Taiwan
5Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
6Department of physics, National Central University, Taoyuan, Taiwan
7School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
* Presenter:Ro-Ya Liu,
Glide mirror symmetry in nonsymmorphic crystals can host the novel hourglass nodal loop state. We present here the band structure of an hourglass semimetal, Nb₃SiTe₆ by means of angle-resolved photoemission spectroscopy. Linear crossing bands at zone boundary were observed, which can be the origin of non-trivial Berry phase, and an example of double quantum spin hall state. These linear band crossings connected and formed a nodal line along the vertical k-path which is slightly different from the theoretical studies. This can be attributed to the weakly bonding of two sublayers by a glide in a unit cell. Moreover, the saddle-like two-dimensional Fermi surface, further band crossings, and parabolic bands were found at the zone center after alkali metal doping. The result is a piece of strong evidence to explain the hall measurement data and gives a hint to the massive nodal loop at the zone center. This study gives an integrated picture of Nb₃SiTe₆ and offers an example of an hourglass material system.

Keywords: Hourglass Dirac semimetal, Dirac nodal line, Glide mirror symmetry, Angle-resolved photoemission spectroscopy, Density functional theory