High-TCsuperconductivity in Cs3C60compounds governed by local Cs-C60Coulomb interactions.
Unique among alkali-doped A3C60fullerene compounds, the A15 and fcc forms of Cs3C60exhibit superconducting states varying under hydrostatic pressure with highest transition temperatures at [Formula: see text]  =  38.3 and 35.2 K, respectively. Herein it is argued that these two compounds under pressure represent the optimal materials of the A3C60family, and that the C60-associated superconductivity is mediated through Coulombic interactions with charges on the alkalis. A derivation of the interlayer Coulombic pairing model of high-TCsuperconductivity employing non-planar geometry is introduced, generalizing the picture of two interacting layers to an interaction between charge reservoirs located on the C60and alkali ions. The optimal transition temperature follows the algebraic expression, TC0=  (12.474 nm2K)/ℓζ, where ℓ relates to the mean spacing between interacting surface charges on the C60and ζ is the average radial distance between the C60surface and the neighboring Cs ions. Values of TC0for the measured cation stoichiometries of Cs3-xC60with x  ≈  0 are found to be 38.19 and 36.88 K for the A15 and fcc forms, respectively, with the dichotomy in transition temperature reflecting the larger ζ and structural disorder in the fcc form. In the A15 form, modeled interacting charges and Coulomb potential e2/ζ are shown to agree quantitatively with findings from nuclear-spin relaxation and mid-infrared optical conductivity. In the fcc form, suppression of [Formula: see text] below TC0is ascribed to native structural disorder. Phononic effects in conjunction with Coulombic pairing are discussed.
Department of Physics, The College of William and Mary, Williamsburg, VA 23187, United States of America.
Dale R
DR
Harshman
Anthony T
AT
Fiory