Optical phonons in the reflectivity spectrum of FeSi

TL;DR

This study investigates the optical phonons in FeSi by measuring its reflectivity across a broad spectrum and temperature range, revealing metallic behavior at high temperatures and a gap opening at low temperatures, with analysis of vibrational modes.

Contribution

It provides experimental data on FeSi's optical phonons and compares observed modes with group theoretical predictions, identifying four out of five expected phonons.

Findings

FeSi exhibits dirty metal-like behavior at room temperature.

A 70 meV energy gap opens at low temperature.

Four of five predicted optical phonons are observed.

Abstract

We measured the reflectivity of a single crystal of FeSi from the far-infrared to the visible region (50-20000 wavenumber), varying the temperature between 4 and 300 K. The optical conductivity function was obtained via Kramers-Kronig analysis. We observed a dirty metal-like behavior at room temperature and the opening of a gap of 70 meV at low temperature. The results of a group theoretical analysis of the lattice vibrational modes are presented and compared to the experimental data. Of the five optical phonons expected for this material only four have been observed in the far-infrared region.