Superconductivity at 5 K in alkali-metal-doped phenanthrene

Abstract

Organic superconductors have π-molecular orbitals, from which electrons can become delocalized, giving rise to metallic conductivity due to orbital overlap between adjacent molecules. Here we report the discovery of superconductivity at a transition temperature (T_c) of ~5 K in alkali-metal-doped phenanthrene. A 1-GPa pressure leads to a 20% increase of T_c, suggesting that alkali-metal-doped phenanthrene shows unconventional superconductivity. Raman spectra indicate that alkali-metal doping injects charge into the system to realize the superconductivity. The discovery of superconductivity in A₃phenanthrene (where A can be either K or Rb) produces a novel broad class of superconductors consisting of fused hydrocarbon benzene rings with π-electron networks. An increase of T_c with increasing number of benzene rings from three to five suggests that organic hydrocarbons with long chains of benzene rings are potential superconductors with high T_c.