Evidence for a purely anionic charge density wave transition in LaAgSb₂

We study the electronic structure of LaAgSb₂, using bulk-sensitive temperature(T)-dependent (20 K – 220 K) Hard X-ray photoemission spectroscopy (HAXPES). LaAgSb₂ exhibits two CDW transitions, one below T₁= 207 K along the crystallographic a-axis, followed by a second CDW transition below T₂= 186 K along the c-axis. Recent studies have identified a Dirac-cone band dispersion and nested Fermi surfaces at T = 16 K, but T-dependent measurements were not reported. We use HAXPES to investigate T-dependent changes in the electronic states of La, Ag and Sb in order to identify states responsible for the CDW transition in LaAgSb₂. HAXPES core level measurements show that the La 3d and Ag 3d core-levels show negligible changes across the CDW transitions. In contrast, Sb 3d core levels show a clear well-separated satellite formation below T₁, and the spectral intensity of the satellite progressively increases on lowering the temperature below T₂. The T-dependence of the Sb 3d satellite feature suggests a second order transition, consistent with the known BCS behavior of T-dependent superlattice reflections by x-ray diffraction. The results indicate a purely anionic character CDW transition, with no direct involvement of the La and Ag cationic derived states in the CDW transition.