Based on first-principles calculations and symmetry analysis, we discovery that the ${\mathrm{Ag}}_2\mathrm{S}$ with $Cmce$ symmetry is a topological nodal-line semimetal in the absence of spin-orbit coupling. A single nodal loop as protected by the glide symmetry exists around the center of the Brillouin zone, dispersing slightly in the momentum space to form both electron and hole pockets around the loop. Moreover, a nearly flat drumheadlike surface state appears on the (001) surface of this material. The nodal-line semimetal phase and its drumheadlike surface states are expected to be experimentally detectable in $Cmce$-phase ${\mathrm{Ag}}_2\mathrm{S}$ because spin-orbit coupling will only open a negligible gap comparing to the energy dispersion of the nodal loop. Our finding provides a different member to the growing family of nodal-line semimetals with a single nodal loop structure.

• Received 15 June 2017

DOI:https://doi.org/10.1103/PhysRevB.96.115106