Raman scattering study of (K$_x$Sr$_{1-x}$)Fe$_2$As$_2$ ($x$ = 0.0, 0.4)

TL;DR

This study uses polarized Raman spectroscopy to analyze phonon modes in SrFe$_2$As$_2$ and K$_{0.4}$Sr$_{0.6}$Fe$_2$As$_2$, revealing no anomalies near structural or superconducting transitions, and models spectra with a shell model.

Contribution

It provides detailed Raman spectra and mode identification for these compounds, and demonstrates the absence of detectable anomalies during phase transitions.

Findings

All four symmetry-allowed phonon modes identified.

Shell model effectively describes the spectra.

No anomalies observed near phase transitions.

Abstract

Polarized Raman spectra of non-superconducting SrFe$_2$As$_2$ and superconducting K$_{0.4}$Sr$_{0.6}$Fe$_2$As$_2$ ($T_c = 37$ K) are reported. All four phonon modes (A$_{1g}$ + B$_{1g}$ + 2E$_g$) allowed by symmetry, are found and identified. Shell model gives reasonable description of the spectra. No detectable anomalies are observed near the tetragonal-to-orthorhombic transition in SrFe$_2$As$_2$ or the superconducting transition in K$_{0.4}$Sr$_{0.6}$Fe$_2$As$_2$.