We have observed evidence of superconductivity at temperatures in the vicinity of 260 K in phosphorus-doped graphite and graphene. This evidence includes transport current, magnetic susceptibility, Hall effect and (pancake) vortex state measurements. All of these measurements indicate a transition which is that of a type II superconductor with no type I phase until below the limits of our measurement capabilities. Vortex states are inferred from periodically repeated steps in the resistance versus temperature characteristics of highly oriented pyrolytic graphite and exfoliated doped multilayer graphene. Magnetic susceptibility measurements have shown results qualitatively similar to those expected (and experimentally observed by others) for ultra-thin (thickness ≪λL) films. The magnetization is negative for field-cooled and zero-field-cooled measurements. The magnetization for field cooled and zero-field-cooled measurements begin to diverge at approximately 260 K. Hall effect measurements show a sign reversal in the Hall voltage as the temperature is reduced from 300 K to 78 K.

The possibility of creating superconductivity in Highly Oriented Pyrolytic Graphite (HOPG) by means of doping was investigated. Bulk HOPG samples were doped with phosphorous using either ion-implantation or by Chemical Vapor Deposition growth with phosphine in the gas mixture. The methods for testing the graphene samples, once doped, were done by performing R vs. T measurements, and determining via observation suppressed superconductive characteristics signaling the presence of the Meissner Effect in a strong applied magnetic field. Before doping, the resistance vs. temperature (R vs. T) characteristic of the HOPG was measured. The R vs. T characteristic was again measured after doping, and for surface multilayers of graphene exfoliated from the post doped bulk sample. A 100 to 350 mT magnetic field was supplied, and the R vs. T characteristic was re-measured on a number of samples.Phosphorous-implanted HOPG samples exhibit deviations from the expected rise in resistance as the temperature is reduced to some point above 100 K. The application of a modest magnetic field reverses this trend. A step in resistance at a temperature of approximately 50-60 K in all of the samples is clearly observed, as well as a second step iv at 100-120 K, a third at a temperature range of 150-180 K and a fourth from about 200-240 K. A response consistent with the presence of magnetic field flux pancake vortices in phosphorous implanted HOPG and in phosphorous-doped exfoliated multilayer graphene has been observed. The lack of zero resistance at low temperatures is also consistent with pancake vortex behaviour in the flux-flow regime. The presence of magnetic vortices requires, and is direct evidence of superconductivity.