Nonsymmorphic symmetry-protected band crossings in a square-net metal PtPb4

Topological semimetals with symmetry-protected band crossings have emerged as a rich landscape to explore intriguing electronic phenomena. Nonsymmorphic symmetries in particular have been shown to play an important role in protecting the crossings along a line (rather than a point) in momentum space. Here we report experimental and theoretical evidence for Dirac nodal line crossings along the Brillouin zone boundaries in PtPb4, arising from the nonsymmorphic symmetry of its crystal structure. Interestingly, while the nodal lines would remain gapless in the absence of spin-orbit coupling (SOC), the SOC, in this case, plays a detrimental role to topology by lifting the band degeneracy everywhere except at a set of isolated points. Nevertheless, the nodal line is observed to have a bandwidth much smaller than that found in density functional theory (DFT). Our findings reveal PtPb4 to be a material system with narrow crossings approximately protected by nonsymmorphic crystalline symmetries.

Automated summary

The study reports Dirac nodal line crossings in PtPb4, which arise from the nonsymmorphic symmetry of its crystal structure. The results show that the nodal lines remain gapless in the absence of spin-orbit coupling (SOC), but the SOC lifts the band degeneracy everywhere except at a set of isolated points. However, the observed nodal line has a smaller bandwidth than predicted by density functional theory (DFT).