Dirac Nodal Line in Hourglass Semimetal Nb₃SiTe₆

Glide-mirror symmetry in nonsymmorphic crystals can foster the emergence of novel hourglass nodal loop states. Here, we present spectroscopic signatures from angle-resolved photoemission of a predicted topological hourglass semimetal phase in Nb₃SiTe₆. Linear band crossings are observed at the zone boundary of Nb₃SiTe₆, which could be the origin of the nontrivial Berry phase and are consistent with a predicted glide quantum spin Hall effect; such linear band crossings connect to form a nodal loop. Furthermore, the saddle-like Fermi surface of Nb₃SiTe₆observed in our results helps unveil linear band crossings that could be missed. In situ alkali-metal doping of Nb₃SiTe₆also facilitated the observation of other band crossings and parabolic bands at the zone center correlated with accidental nodal loop states.