In-Situ Infrared Transmission Study of Rb- and K-Doped Fullerenes

TL;DR

This study investigates how doping with potassium and rubidium affects the infrared vibrational spectra of C60 fullerenes, revealing phase transitions and electron-phonon coupling details.

Contribution

It provides the first in-situ IR transmission measurements of doped fullerenes, identifying distinct phases and analyzing vibrational mode shifts with doping levels.

Findings

Four distinct phases identified at specific doping levels.

Significant downward shifts in vibrational frequencies with doping.

Quantitative analysis of electron-phonon coupling for a key IR mode.

Abstract

We have measured the four IR active $C_{60}$ molecular vibrations in $M_{x}C_{60}$ $(M = K, Rb)$ as a function of doping $x$. We observe discontinuous changes in the vibrational spectra showing four distinct phases (presumably $x = 0, 3, 4$, and 6). The $1427cm^{-1}$ and $576cm^{-1}$ modes show the largest changes shifting downward in frequency in four steps as the doping increases. Several new very weak modes are visible in the $x=6$ phase and are possibly Raman modes becoming weakly optically active. We present quantitative fits of the data and calculate the electron-phonon coupling of the $1427cm^{-1}$ IR mode.