The role of phonon- and photon-coupled interactions in electron pairing in solid state materials

The essential role of the phonon- and photon-coupled interactions in the electron pairing in the macroscopic sized conventional superconductivity is investigated by comparing the conventional superconductivity in the macroscopic sized materials with the nondissipative diamagnetic currents in the negatively charged small sized molecules such as cyclopentadiene monoanion (5an−) and cyclobutadiene dianion (4an2−). The nondissipative diamagnetic currents in the negatively charged small sized molecules such as 5an− and 4an2− cannot be explained by the Bardeen–Cooper–Schrieffer (BCS) theory because attractive phonon-coupled interactions between two electrons (V6π,N,BCS,phonon,e–e) are zero and direct electron–electron repulsion (V6π,N,BCS,repulsive,e–e) becomes very large. However, these phenomena in 5an− and 4an2− can be well explained by the photon-coupled interactions between all nuclei and electrons. The phonon-coupled interactions (Vphonon,e–e) play an essential role in the forming of the closed-shell electronic structures with finite valence–conduction band gaps, in which two electrons occupying the same orbitals with opposite momentum and spins become stable, and the photon-coupled interactions (Vmacro,photon,N,j,σ) play an essential role in attractive interactions between these two electrons. Because of the photon-coupled interactions as well as the phonon-coupled interactions, electron pairs can be formed in the macroscopic sized materials, and the conventional superconducting states can appear below the superconducting critical temperature (Tc). Our molecular perspective suggested in this article is compared with the BCS theory, and the reason why the conventional superconductivity has been excellently explained by the BCS theory is also discussed.