Electron-phonon interactions and superconductivity in K3C60

Using electronic states and phonon states from first-principles calculations on K3C60 to evaluate the quantities in the McMillan equation, we examine the effects of both electron-phonon dynamic charge coupling (Q) and Jahn-Teller coupling (JT) on various superconducting properties, including Tc, ΔTc (the shift of Tc for 1 GPa pressure), αC (the isotope exponent for →1312C), and αK (the isotope exponent for →4139K). All quantities including electron-phonon coupling are evaluated (without modification) directly from theory, except for the screening length between conducting electrons and ions, Rsc. With Rsc=0.8-1.0, we find that the calculated properties, Tc, ΔTc, and αC, are all in good agreement with experimental measurements. We find that the superconducting properties depend critically upon the synergy between Q and JT coupling.