Discovery of superconductivity in K-doped 2,2-bipyridine

Organic compounds are always promising candidates of superconductors with high transition temperatures. The 2,2 '-bipyridine solely composed by C, H, and N atoms is examined for this proposal. The presence of Meissner effect with a transition temperature of 7.2 K in this material upon potassium doping is demonstrated by the dc magnetic susceptibility measurements. The real part of the ac susceptibility exhibits the same transition temperature as that in dc magnetization, and a sharp peak appeared in the imaginary part indicates the formation of the weakly linked superconducting vortex current. The occurrence of superconductivity is further supported by the resistance drop at the transition together with its suppression by the applied magnetic fields. The superconducting phase is identified to be K3-2,2 '-bipyridine with P21 space-group from the analysis of Raman scattering spectra and X-ray diffraction patterns as well as the first-principles calculations. This work not only opens an encouraging window for finding superconductivity after optoelectronics in 2,2 '-bipyridine-based materials but also offers an example to realize superconductivity from conducting polymers and their derivatives.