Superconducting Characteristics of a Graphite/N-Alkane Mixture above Room Temperature

Abstract

The resistance of a pitch-based carbon fiber/n-alkane (n-C_kH_2k+2, k = 8, 9, 10, 12, 13, and 16) mixture in a heated Teflon tube was measured using a two-terminal measurement. The results showed that the resistance suddenly increased at temperatures between 367.77 and 504.24 K (T_increase), and that the amount of change in resistance at T_increase varied by two orders of magnitude between the samples. Measurements and calculations revealed that n-alkanes did not reach their boiling points at T_increase, indicating that this rapid increase in resistance was a property of the mixture. The extremely large resistance range of the mixture after the sudden resistance increase is due to the change in the aspect ratio of the carbon fibers. However, these large variations were not observed below T_increase, suggesting that n-alkanes dramatically reduce the resistance of the mixture below T_increase. The sudden increase in resistance at T_increase and the alkane effect support the hypothesis that T_increase is the critical temperature for superconductivity. The larger is the average aspect ratio of the carbon fiber, i.e., the larger are the sides of the fiber (graphite basal surface), the higher is the T_increase. Therefore, adsorption of n-alkanes onto the graphite basal surface increases T_increase (T_c), which is consistent with the prediction made by Ginzburg's theory of surface superconductivity. Based on Ginzburg's theory, the appearance of room temperature superconductivity in mixtures of graphite and n-alkane was attributed to a remarkable fit between the hydrogen atoms bonded to one side of the zigzag carbon chain of n-alkane and the hexagonal center formed by the carbon atoms on the graphite basal plane.