Nonadiabatic superconductivity in Li-intercalated hexagonal boron nitride bilayer

Abstract

In the case of Li-intercalated hexagonal boron nitride bilayer (Li-hBN), the vertex corrections of electron-phonon interaction cannot be omitted. This is evidenced by the very high value of the ratio $\lambda {\omega }_D/{\epsilon }_F\sim 0.46$, where $\lambda$ is the electron-phonon coupling constant, ${\omega }_D$ is the Debye frequency, and the symbol ${\epsilon }_F$ represents the Fermi energy. Due to the nonadiabatic effects, the phonon-induced superconducting state in Li-hBN is characterized by the much lower value of critical temperature ($T_C^{\mathrm{LOVC}}\in \{19.1,15.5,11.8\}$ K, for ${\mu }^{\star }\in \{0.1,0.14,0.2\}$), than would result from calculations not taking this effect into account: $T_C^{\mathrm{ME}}\in \{31.9,26.9,21\}$ K. From the technological point of view, the low value of $T_C$ limits the possible applications of Li-hBN superconducting properties. The calculations were carried out under the classic Migdal-Eliashberg formalism (ME) and the Eliashberg theory with the lowest-order vertex corrections (LOVC).

8 pages, 5 figures