Optimal High-T_c Superconductivity in Cs₃C₆₀

Optimal High-T_C Superconductivity in Cs₃C₆₀, D. R. Harshman and A. T. Fiory

The highest superconducting transition temperatures in the (A_1-xB_x)₃C₆₀ superconducting family are seen in the A15 and FCC structural phases of Cs₃C₆₀ (optimized under hydrostatic pressure), exhibiting measured values for near-stoichiometric samples of T_C0^meas. = 37.8 K and 35.7 K, respectively. It is argued these two Cs-intercalated C₆₀ compounds represent the optimal materials of their respective structures, with superconductivity originating from Coulombic e–h interactions between the C₆₀ molecules, which host the n-type superconductivity, and mediating holes associated with the Cs cations. A variation of the interlayer Coulombic pairing model [Harshman and Fiory, J. Supercond. Nov. Magn. 28, 2967 (2015), and references therein] is introduced in which T_C0^calc. ∝ 1/ℓζ where ℓ relates to the mean spacing between interacting charges on surfaces of the C₆₀ molecules, and ζ is the average radial distance between the surface of the C₆₀ molecules and the neighboring Cs cations. For stoichiometric Cs₃C₆₀, T_C0^calc. = 38.08 K and 35.67 K for the A15 and FCC macrostructures, respectively; the dichotomy is attributable to differences in ζ.

Dale R. Harshman and Anthony T. Fiory, APS Meeting (abstract: MAR16-2015-004113), Baltimore, Maryland, 14-18 March 2016 (slides).