Electron-phonon interaction in the solid form of the smallest fullerene C$_{20}$

TL;DR

This study calculates the electron-phonon coupling in a theoretical carbon phase made of C20 fullerenes, predicting potential superconductivity with a transition temperature up to 55 K.

Contribution

It provides first-principles calculations of electron-phonon interactions in a novel C20-based fullerene structure, suggesting possible superconductivity.

Findings

Electron-phonon coupling constant in NaC22 is 0.28 eV.

Predicted superconducting T_c ranges from 15 to 55 K.

The structure's larger curvature enhances electron-phonon interaction.

Abstract

The electron-phonon coupling of a theoretically devised carbon phase made by assembling the smallest fullerenes C$_{20}$ is calculated from first principles. The structure consists of C$_{20}$ cages in an {\it fcc} lattice interlinked by two bridging carbon atoms in the interstitial tetrahedral sites ({\it fcc}-C$_{22}$). The crystal is insulating but can be made metallic by doping with interstitial alkali atoms. In the compound NaC$_{22}$ the calculated coupling constant $\lambda/N(0)$ is 0.28 eV, a value much larger than in C$_{60}$, as expected from the larger curvature of C$_{20}$. On the basis of the McMillan's formula, the calculated $\lambda$=1.12 and a $\mu^*$ assumed in the range 0.3-0.1 a superconducting T$_c$ in the range 15-55 K is predicted.