Anomalous Raman scattering from phonons and electrons of superconducting FeSe$_{0.82}$

TL;DR

This study investigates temperature-dependent Raman spectra of FeSe$_{0.82}$, revealing anomalies linked to spin-phonon coupling and electronic orbital transitions, supported by first-principles calculations.

Contribution

It provides new insights into the coupling between phonons, electrons, and magnetic order in FeSe$_{0.82}$ through combined experimental and theoretical analysis.

Findings

Phonon mode near 100 cm$^{-1}$ increases in frequency below 100 K.

High frequency modes at 1350 cm$^{-1}$ and 1600 cm$^{-1}$ linked to electronic orbital transitions.

Evidence of strong spin-phonon coupling and orbital-related electronic Raman scattering.

Abstract

We report interesting anomalies in the temperature dependent Raman spectra of FeSe$_{0.82}$ measured from 3K to 300K in the spectral range from 60 to 1800 cm$^{-1}$ and determine their origin using complementary first-principles density functional calculations. A phonon mode near 100 cm$^{-1}$ exhibits a sharp increase by $\sim$ 5% in frequency below a temperature T$_s$ ($\sim$ 100 K) attributed to strong spin-phonon coupling and onset of short-range antiferromagnetic order. In addition, two high frequency modes are observed at 1350 cm$^{-1}$ and 1600 cm$^{-1}$, attributed to electronic Raman scattering from ($x^2-y^2$)to $xz$ / $yz$ $d$-orbitals of Fe.