  Superconductivity without phonons has been proposed for strongly correlated
electron materials that are tuned close to a zero-temperature magnetic
instability of itinerant charge carriers. Near this boundary, quantum
fluctuations of magnetic degrees of freedom assume the role of phonons in
conventional superconductors, creating an attractive interaction that glues
electrons into superconducting pairs. Here we show that superconductivity can
arise from a very different spectrum of fluctuations associated with a local or
Kondo-breakdown quantum-critical point that is revealed in isotropic scattering
of charge carriers and a sub-linear temperature-dependent electrical
resistivity. At this critical point, accessed by applying pressure to the
strongly correlated, local-moment antiferromagnet CeRhIn5, magnetic and charge
fluctuations coexist and produce electronic scattering that is maximal at the
optimal pressure for superconductivity. This previously unanticipated source of
pairing glue opens possibilities for understanding and discovering new
unconventional forms of superconductivity.
