Superconductivity in A1.5phenanthrene (A=Sr, Ba)

We discover superconductivity in alkali-earth metal-doped phenanthrene. The superconducting critical temperatures T-c are 5.6 and 5.4 K for Sr(1.5)phenanthrene and Ba(1.5)phenanthrene, respectively. The shielding fraction of Ba1.5phenanthrene exceeds 65%. The Raman spectra show 8 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 a larger lattice indicates unconventional superconductivity in this organic system.