Magnetic Transitions in K-Doped Biphenyl and ${p}$ -Terphenyl

Recently, an interesting superconductivity of the transition temperatures range from 7.2 to 43 K and then to 123 K in K-doped ${p}$ -terphenyl was reported, which attracts much attention. In this paper, to identify the superconducting phase from chemical component, we have investigated the crystal structures and electronic and magnetic properties in the cases of K-doped biphenyl and ${p}$ -terphenyl based on the first-principles calculations. We found that the change of doping concentration results in a series of magnetic transitions. Pristine biphenyl and ${p}$ -terphenyl are both nonmagnetic (NM) semiconductors. Doping one K atom for each organic molecule, the system exhibits the antiferromagnetism. With increasing the doping concentration of K atoms, however, the spin ordering disappears and the compound behaviors as the NM metal. Thus, we suggest that the superconducting phases observed experimentally are corresponding to the highly doping levels, which will deepen the understanding of the superconductivity of aromatic hydrocarbons.