The sharp resistive transitions in superconducting single crystals of natural abundance and 99% 13 C-enriched Rb 3 C 60 reveal the carbon isotope effect with unprecedented accuracy. The measured isotope exponent α C =0.21±0.012 is outside the error bars of all previous reported values. Our precise value for α C , combined with T c , α Rb , 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)