Phononic self-energy effects and superconductivity in CaC6

Abstract

We study the graphite intercalated compound CaC6 by means of Eliashberg theory. We perform an analysis of the electron-phonon coupling and define a minimal 6-band anisotropic structure, that leads to a Fermi surface dependance of the superconducting gap. A comparison of the superconducting gap structure obtained using the Eliashberg and the superconducting density functional theory is performed. We further report the anisotropic properties of the electronic spectral function, the polaronic quasi-particle branches and their interplay with Bogoljubov excitations.

Anisotropic Migdal-Eliashberg theory using Wannier functions

“…(21), (22) and µ * c =0. 16. Figure 6(b) shows the real part of the superconducting gap function along the real energy axis, as obtained from the imaginary axis solutions of Fig 6(a) via the approximate analytic continuation using Padé functions.…”

“…However relaxing this constraint would also introduce one additional equation [Eq. (16)] in order to calculate the correct quasiparticle shifts and impose the conservation of charge in the system.…”

Isotropic and anisotropic description of superconducting state in CaC6 compound

“…The matrix of the Coulomb pseudopotentials has been calculated in the next step: Let us note that the parameter μ 3 is equal to 0.21 [35], whereas the electron density of states vector has the following form [17]:…”

Ab initiotheory of superconductivity in a magnetic field. I. Spin density functional theory for superconductors and Eliashberg equations

“…that is evaluated to We obtain the Eliashberg equations similar to their usual, spin-degenerate form 26,60 , that only refer to the GF implicitly …”

“…The interacting system is also being investigated directly by means of a magnetic extension of the Eliashberg method [24][25][26][27][28] . A derivation 29 of this alternative approach in the present notation is given in Sec.…”