Probing the Superconductivity Limit of Li‐Doped Graphene

AbstractThe introduction of superconductivity in graphene systems is highly desirable from both fundamental physics and application perspectives. In this article, a superlattice strategy to develop a series of Li‐doped graphene is reported: deposition type‐I (Li2C6, Li2C8, LiC6, Li3C24, LiC12, LiC16, Li2C36, LiC24), intercalation type‐II (LiC4, Li2C12, LiC8, LiC12, LiC16), and coexisting deposition and intercalation type‐III (Li3C12). With increasing concentration of Li atoms, both metallicity, and electron–phonon coupling (EPC) has dramatically increased, which is favorable for the emergence of superconductivity in the screened Li–C compounds. Notably, graphene superlattice structures with intercalated Li2 atoms have higher stability, while Li1‐deposited graphene at the same concentration produces higher Tc. Among them, type‐I‐Li2C6, type‐I‐Li2C8, type‐II‐LiC4, and type‐III‐Li3C12 are phonon‐mediated superconductors with high transition temperatures (Tc) of 18, 12, 3.4, and 14 K, respectively. The EPC of type‐I‐Li2C6, type‐I‐Li2C8, and type‐III‐Li3C12 mainly arises from the coupling of the C‐2pz electron states with the low‐frequency (0–800 cm−1) deposition‐Lixy/Liz, and out‐of‐plane‐Cz vibrations. In contrast, the high‐frequency (800–1600 cm−1) vibration modes of in‐plane‐Cxy atoms are mainly responsible for the Tc of type‐II‐LiC4. The findings provide comprehensive insights into the superconductivity limit of Li‐doped graphene.