The sharp resistive transitions in superconducting single crystals of natural abundance and 99% 13C-enriched Rb3C60 reveal the carbon isotope effect with unprecedented accuracy. The measured isotope exponent αC=0.21±0.012 is outside the error bars of all previous reported values. Our precise value for αC, combined with Tc, αRb, and an ab initio calculation of the frequency distribution of the electron-phonon coupling, allows a fully constrained determination of the coupling strength λ=0.9+0.15−0.1 and the Coulomb repulsion μ∗=0.22+0.03−0.02. These new measurements reveal a phonon-mediated superconductor with moderate coupling to a wide range of phonons centered near ∼1400K.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)