Charge transfer in alkaline-earth metal graphite intercalation compounds

The charge transfer from a metal atom towards the carbon layers in first stage graphite intercalation compounds (GIC) is a fundamental issue to explain under which conditions superconductivity sets in and the electronic properties of such ground state. To study in detail the transfer process and its evolution as a function of the nature of the intercalated metal, and especially taking in consideration the interlayer distance, we performed detailed X-Ray Diffraction and Raman scattering measurements on very high-quality bulk intercalated CaC6, SrC6 and BaC6 samples. We combined both the experimental results with detailed density functional theory calculations to give a coherent picture in which it is possible to follow the evolution of the charge transfer to the carbon layer in full agreement with the experimental data. The full comprehension of such mechanism remains a fundamental issue to explain the variation of the superconducting ground state in first stage GIC.