Superconductivity in potassium-doped organic materials*

Abstract: Recent discoveries demonstrated that organic materials could be candidates for high temperature superconductors. In aromatic hydrocarbons, superconducting transition temperatures were observed up to 33 K, while in potassium-doped p-terphenyl and p-quaterphenyl, there were signatures indicating Tc of 120K. These results clearly indicate that organic materials are potential high temperature superconductors. However, the accurate amount of doped electrons and their positions have not been established experimentally, nor has any consensus reached for its superconducting mechanism. Here, we report the systematic studies of the crystal structures, charge transfer, electronic structures, electron-phonon interactions, magnetism, electronic correlations, and pressure effects in potassium-doped organic materials. Our calculations show that there exists a unified superconducting phase in the same 5-7 K range for all molecules containing benzene rings. Doping two electrons in the near constant density of states at the Fermi level accounts for this unified phase. The materials exhibit multiple superconducting phases and the high density of states at Fermi level upon 2+x-electron doping is responsible. The roles of doping content, electronic correlations, and pressure effect on superconductivity are emphasized.