Lattice dynamics of the topological Dirac semimetal LaAgSb₂ with charge density wave ordering

Abstract

LaAgSb₂ is a rare material that offers the opportunity to investigate the complex interplay between charge density wave (CDW) ordering and topology-protected electronic band structure. As both of these phenomena are governed by the structural symmetries, a comprehensive study of the lattice dynamics is highly desirable. In this paper, we present the results of temperature- and pressure-dependent Raman spectroscopy and x-ray diffraction in single crystalline LaAgSb₂. Our results confirm that Raman spectroscopy is a highly sensitive tool to probe the CDW-ordering phenomenon, particularly the low-temperature second CDW transition in LaAgSb₂ , which appears as a very weak anomaly in most experiments. The crystal-orientation-dependent measurements provide the evolution of Raman modes with crystallographic symmetries and can be further studied through group symmetry analysis. The low-temperature x-ray diffraction data show the emergence of structural modulations corresponding to the CDW instability. The combined high-pressure Raman spectroscopy and synchrotron x-ray diffraction reveal multiple structural phase transitions through lowering of crystalline symmetries, which are also expected to lead to electronic topological transitions.