Anisotropic Electron-Phonon Coupling and Dynamical Nesting on the Graphene Sheets in CaC6

TL;DR

This study reveals unexpectedly strong electron-phonon coupling on graphene sheets in CaC6, suggesting that graphene's vibrational interactions significantly contribute to its superconductivity, challenging previous theoretical models.

Contribution

First experimental investigation of electronic structure in CaC6 showing strong EPC on graphene sheets, highlighting their role in superconductivity.

Findings

Strong electron-phonon coupling on graphene-derived Fermi sheets

Graphene vibrations interact with high frequency, influencing pairing

Graphene sheets can support superconductivity in doped compounds

Abstract

Superconductivity in graphite intercalated compounds has been studied for more than 40 years and it is still not fully understood, despite the recent progress and the discovery of relatively high Tc superconductivity in CaC6 and YbC6. Recent studies now suggest that the electron-phonon coupling is most likely responsible for pairing and that the intercalant-derived electronic states and vibrations play the dominant role. Here, we present the first studies of electronic structure in CaC6, a superconductor with Tc=11.6 K. Using angle-resolved photoemission spectroscopy, we find that, contrary to theoretical models, the EPC on the graphene-derived Fermi sheets is surprisingly strong, reflecting the interaction with high-frequency graphene-derived vibrations. Thus, in addition to the amazing properties in the charge-neutral state, graphene sheets also show surprises in the heavily doped regime: they may support strong pairing interactions and lead to superconductivity in compounds in which they are building blocks.