Raman scattering from a superconductivity-induced bound state in $MgB_2$

TL;DR

This paper explains the origin of a sharp Raman peak in superconducting MgB2 as a bound state from electron-phonon interactions, clarifying its symmetry and band-specific appearance.

Contribution

It provides a theoretical explanation for the superconductivity-induced bound state observed in MgB2's Raman spectrum, including effects of impurity scattering.

Findings

The peak is due to a bound state caused by electron-phonon coupling.

The peak appears only in E2g symmetry spectra and in sigma bands.

Impurity scattering effects on the bound state are analyzed.

Abstract

It is shown that the sharp peak in the $E_{2g}$ Raman spectrum of superconducting $MgB_2$ is due to a bound state caused by the electron-phonon coupling. Our theory explains why this peak appears only in the spectra with $E_{2g}$ symmetry and only in the $\sigma$ but not $\pi$ bands. The properties of the bound state and the Raman spectrum are investigated, also in the presence of impurity scattering.