Topological electride of t -YCl

Topological electrides have attracted extensive attention, not only serving as good platforms for studying Dirac fermion, Weyl fermion, and diverse quasiparticles beyond the Dirac and Weyl fermions, but also hosting rich physical and chemical properties such as low work function, high conductivity, and high electron mobility. Motivated by the synthesized YCl and Y2Cl3 electrides with nontrivial topology, we have explored the Y-Cl binary system under pressure. Based on the first-principles calculations and crystal-structure prediction techniques, we find a t-YCl phase with the space group of P4/ that is both thermodynamically and lattice dynamically stable, and also recoverable to the ambient condition. Based on the k·p method and irreducible representation analyses, we propose that t-YCl has a topological nodal chain surrounding the Z point in the Brillouin zone without spin-orbit coupling (SOC), and evolves into a Dirac semimetal phase with two Dirac points protected by R4z symmetry when taking SOC into consideration. In addition, based on the band representation (BR) analyses, we find the highest occupied bands belong to A1@2a BR. Since both the Y and Cl atoms occupy the 2c Wyckoff positions, i.e., no atom in t-YCl system locates at the 2a Wyckoff positions, it thus suggests the unconventional nature of an uncompensated state at the 2a Wyckoff position. Remembering the ionic compound nature, the unconventional t-YCl phase hosts great potential to be an electride material, which has been further verified by our electron localization function calculations, with the uncompensated state at 2a Wyckoff position contributed by the interstitial quasiatoms. Our work provides a good theoretical and experimental platform for the study of pressure-induced topological electride states.