Superconductivity in Hydrogenated Graphites

We report transport and magnetization measurements on graphites that have been hydrogenated by intercalation with an alkane (octane). The temperature-dependent electrical resistivity shows anomalies manifested as reentrant insulator-metal transitions. Below T ∼ 50 K, the magnetoresistance data shows both antiferromagnetic (AFM) and ferromagnetic (FM) behavior as the magnetic field is decrease or increased, respectively. The system is possibly an unconventional magnetic superconductor. The irreversibility observed in the field-cooled vs. the zero-field cooled data for a sufficiently high magnetic field suggests that the system might enter a superconducting state below Tc ∼ 50 K. Energy gap data is obtained from nonlocal electric differential conductance measurements. An excitonic mechanism is likely driving the system to the superconducting state below the same T ∼ 50 K, where the gap is divergent. We find that the hydrogenated carbon fiber is a multiple gap system with critical temperatures estimates above room temperature. The temperature dependence of the superconducting gap follows the flat-band energy relationship, with the flat band gap parameter linearly increasing with the temperature above Tc ∼ 50 K. Thus, we find that either a magnetic or an electric field can drive this hydrogenated graphitic system to superconducting state below Tc ∼ 50 K. In addition, AF spin fluctuations creates pseudogap states above Tc ∼ 50 K.