The Strong-Coupling Character of Superconducting Phase in Heavily-Doped cg-C4H4

Abstract

Hydrocarbon compounds have recently been considered as highly promising materials for phonon-mediated superconductors, exhibiting high values of critical temperature (T_C) in ambient pressure. In this study, we present a quantitative characterization of the superconducting properties of heavily-doped cg-C₄H₄. By using the Migdal–Eliashberg formalism, we demonstrate that the critical temperature in this material is relatively high (T_C = 96.54 K) assuming that the Coulomb pseudopotential takes a value of 0.1. Furthermore, the used theoretical model allows for the characterization of other essential thermodynamic properties, such as the superconducting band gap, free energy, specific heat, and critical magnetic field. We observe that the characteristic thermodynamic ratios for the above-mentioned parameters differ from the predictions of the Bardeen–Cooper–Schrieffer theory. Our analysis suggests that strong-coupling and retardation effects play a crucial role in the discussed superconducting state, which cannot be described within the weak-coupling regime.