Signatures of nonadiabatic superconductivity in lithium-decorated graphene

Recent studies confirmed that the long-searched-for phonon-mediated superconducting phase in graphene may be induced via lithium deposition. However, it is also suggested that lithium-decorated graphene (LiC6) behaves as a canonical superconductor, despite the moderate electron-phonon coupling constant and low Fermi energy in this material. Herein, this issue is addressed within the isotropic Eliashberg formalism in the adiabatic and nonadiabatic regimes to account for the potentially pivotal effects hitherto not captured. The conducted analysis indicates signatures of the nonadiabatic superconductivity in LiC6 and the resulting effects on the selected thermodynamic properties. It is shown that although the critical temperature obtained in the nonadiabatic regime is similar to the earlier estimates (similar to 6 K), its value corresponds to the smaller magnitude of the Coulomb pseudopotential than previously expected. Moreover, the characteristic ratio of the pairing gap and the inverse temperature is found to notably exceed estimates of the BCS theory. In what follows, the obtained results attempt to present coherent interpretation of the superconducting phase in LiC6 and vital insight into its fundamental properties. Moreover, they allow us to draw potential directions for future research on low-dimensional superconductivity by reveling that many other graphene-related superconductors may be subject to nonadiabatic effects. This aspect appears to be essential for the design of new two-dimensional hexagonal superconductors aimed at relatively high critical temperature values.