# Raman phonons in the ferroelectric-like metal LiOsO$_3$

## TL;DR

This study uses Raman scattering to analyze phonon modes in LiOsO$_3$, revealing a continuous order-disorder transition that supports the coexistence of ferroelectricity and metallicity.

## Contribution

It provides a systematic assignment of Raman-active phonon modes in both phases and clarifies the nature of the structural transition in LiOsO$_3$.

## Key findings

- Observation of 4 Raman peaks in the centrosymmetric phase.
- Observation of 12 Raman peaks in the non-centrosymmetric phase.
- Continuous evolution of Raman frequencies indicates an order-disorder transition.

## Abstract

The novel ferroelectric-like structural transition observed in metallic LiOsO$_3$ [Y. Shi et al., Nat. Mater. 12, 1024 (2013)], has invoked many theoretical and experimental interests. In this work, we have performed polarized and temperature-dependent Raman scattering measurements on high-quality single crystal LiOsO$_3$ and identified Raman-active modes in both centrosymmetric phase (300 K, R$\bar{3}$c) and non-centrosymmetric phase (10 K, R3c). Only four phonon peaks are observed in the former phase, while there are twelve peaks in the latter phase because of the reduction of crystal symmetry. With the help of careful symmetry analysis and first-principles calculations, we can make a systematic assignment for the observed Raman modes in both phases. The significant changes in line-width and the continuous evolution of Raman frequencies with temperatures were observed for the E$_g$ modes around the transition temperature, which suggests that the ferroelectric-like structural transition is a continuous order-disorder transition. The result sheds light on the coexistence of ferroelectricity and metallicity in the compound.