Electronic Structure of Superconducting ${\mathrm{KC}}_{8}$ and Nonsuperconducting ${\mathrm{LiC}}_{6}$ Graphite Intercalation Compounds: Evidence for a Graphene-Sheet-Driven Superconducting State

Electronic Structure of Superconducting ${KC}_{8}$ and Nonsuperconducting ${LiC}_{6}$ Graphite Intercalation Compounds: Evidence for a Graphene-Sheet-Driven Superconducting State

Z.-H. Pan, J. Camacho, M. H. Upton, A. V. Fedorov, C. A. Howard, M. Ellerby, and T. Valla

Phys. Rev. Lett. 106, 187002 – Published 6 May 2011

Abstract

We have performed photoemission studies of the electronic structure in ${LiC}_{6}$ and ${KC}_{8}$ , a nonsuperconducting and a superconducting graphite intercalation compound, respectively. We have found that the charge transfer from the intercalant layers to graphene layers is larger in ${KC}_{8}$ than in ${LiC}_{6}$ , opposite of what might be expected from their chemical composition. We have also measured the strength of the electron-phonon interaction on the graphene-derived Fermi surface to carbon derived phonons in both materials and found that it follows a universal trend where the coupling strength and superconductivity monotonically increase with the filling of graphene $π^{*}$ states. This correlation suggests that both graphene-derived electrons and graphene-derived phonons are crucial for superconductivity in graphite intercalation compounds.

Received 20 March 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.187002

Authors & Affiliations

Z.-H. Pan¹, J. Camacho¹, M. H. Upton², A. V. Fedorov³, C. A. Howard⁴, M. Ellerby⁴, and T. Valla^1,*

¹Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, New York 11973, USA
²Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60192, USA
³Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
⁴London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom