Lattice dynamics of topological Dirac semimetal LaAgSb$_{2}$ with charge density wave ordering

TL;DR

This study investigates the lattice dynamics of LaAgSb$_{2}$, revealing how charge density wave ordering interacts with its topological electronic structure through temperature and pressure-dependent Raman spectroscopy and x-ray diffraction.

Contribution

It provides a comprehensive analysis of LaAgSb$_{2}$'s lattice dynamics, highlighting the sensitivity of Raman spectroscopy to CDW transitions and identifying multiple structural phase transitions under pressure.

Findings

Raman spectroscopy detects the weak second CDW transition.

Structural modulations emerge at low temperatures.

Multiple phase transitions occur under high pressure.

Abstract

LaAgSb$_{2}$ is a rare material, which 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 report, we present the results of temperature and pressure dependent Raman spectroscopy and x-ray diffraction in single crystalline LaAgSb$_{2}$. Our results confirm that Raman spectroscopy is a highly sensitive tool to probe CDW ordering phenomenon, particularly the low-temperature second CDW transition in LaAgSb$_{2}$, 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.