Discovery of Dirac nodal line in non-symmorphic semimetal Nb₃SiTe₆

Ro-Ya Liu^1,2,3,5*, Angus Huang⁴, Raman Sankar², Shih-Chang Weng⁵, Meng-Kai Lin^1,6, 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, email:liu.roya@nsrrc.org.tw

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