Electron-phonon interaction in Graphite Intercalation Compounds

TL;DR

This paper investigates the electron-phonon interactions in graphite intercalation compounds, revealing a significant dormant interaction between interlayer and π* electrons that correlates with superconductivity, challenging previous simplified models.

Contribution

It introduces a simple model that captures the essential electron-phonon interactions in GICs, highlighting the role of interlayer and π* electrons in superconductivity.

Findings

Identifies strong dormant electron-phonon interactions in GICs.

Provides a geometrical explanation using NMTO Wannier-like functions.

Explains the correlation between interlayer band filling and superconductivity.

Abstract

Motivated by the recent discovery of superconductivity in Ca- and Yb-intercalated graphite (CaC$_{6}$ and YbC$_{6}$) and from the ongoing debate on the nature and role of the interlayer state in this class of compounds, in this work we critically study the electron-phonon properties of a simple model based on primitive graphite. We show that this model captures an essential feature of the electron-phonon properties of the Graphite Intercalation Compounds (GICs), namely, the existence of a strong dormant electron-phonon interaction between interlayer and $\pi ^{\ast}$ electrons, for which we provide a simple geometrical explanation in terms of NMTO Wannier-like functions. Our findings correct the oversimplified view that nearly-free-electron states cannot interact with the surrounding lattice, and explain the empirical correlation between the filling of the interlayer band and the occurrence of superconductivity in Graphite-Intercalation Compounds.