Superconductivity in alkali-earth metals doped phenanthrene

Abstract

We discover superconductivity in alkali-earth metals doped phenanthrene. The superconducting critical temperatures \emph{T}${}_c$ are 5.6 K and 5.4 K for Sr${}_{1.5}$phenanthrene and Ba${}_{1.5}$phenanthrene, respectively. The shielding fraction of Ba${}_{1.5}$phenanthrene exceeds 65%. The Raman spectra show 8 cm${}^{-1}$/electron and 7 cm${}^{-1}$/electron downshifts for the mode at 1441 cm${}^{-1}$ due to the charge transfer to organic molecules from the dopants of Ba and Sr. Similar behavior has been observed in A${}_3$phenanthrene and A${}_3$C${}_{60}$(A = K and Rb). The positive pressure effect in Sr${}_{1.5}$phenanthrene and Ba${}_{1.5}$phenanthrene together with the lower $T_c$ with larger lattice indicates unconventional superconductivity in this organic system.

4 pages, 4 figures