Observation of Meissner effect in potassium-doped $p$-quaterphenyl

Inspired by the discovery of high temperature superconductivity in potassium-doped $p$-terphenyl, we examine the possibility of superconductivity in $p$-quaterphenyl with one more phenyl ring than $p$-terphenyl. The Meissner effect with critical temperatures ranging from 3.5 K to 120 K is found by the magnetic susceptibility measurements in $p$-quaterphenyl upon doping potassium in the condition of annealing or just pestling. The primary superconducting phase with critical temperature of 7.2 K can be reduplicated in several superconducting samples. In both the annealed and pestled superconducting samples, the observation of bipolaronic character by the Raman scattering measurements reveals the close relationship between bipolarons and superconductivity. The occurrence of superconductivity in potassium-doped $p$-quaterphenyl provides an indication that chain link organic molecules are potential candidates for high temperature superconductors.
Comment: 6 pages, 3 figures