Raman response of Stage-1 graphite intercalation compounds revisited

TL;DR

This study uses detailed in-situ Raman spectroscopy to analyze stage-1 graphite intercalation compounds, revealing vibrational modes and electron-phonon coupling constants, and suggesting Raman modes alone do not explain superconductivity.

Contribution

It provides a comprehensive Raman analysis of GICs, assigning vibrational modes and quantifying electron-phonon coupling, challenging previous assumptions about their role in superconductivity.

Findings

Identified four main Raman components between 1200-1700 cm-1.

Determined electron-phonon coupling constant {5}ph < 0.06.

Raman active modes are insufficient to explain superconductivity.

Abstract

We present a detailed in-situ Raman analysis of stage-1 KC8, CaC6, and LiC6 graphite intercalation compounds (GIC) to unravel their intrinsic finger print. Four main components were found between 1200 cm-1 and 1700 cm-1, and each of them were assigned to a corresponding vibrational mode. From a detailed line shape analysis of the intrinsic Fano-lines of the G- and D-line response we precisely determine the position ({\omega}ph), line width ({\Gamma}ph) and asymmetry (q) from each component. The comparison to the theoretical calculated line width and position of each component allow us to extract the electron-phonon coupling constant of these compounds. A coupling constant {\lambda}ph < 0.06 was obtained. This highlights that Raman active modes alone are not sufficient to explain the superconductivity within the electron-phonon coupling mechanism in CaC6 and KC8.