  Identifying the mechanism of superconductivity in the high-temperature
cuprate superconductors is one of the major outstanding problems in physics. We
report local measurements of the onset of superconducting pairing in the
high-transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+d using a
lattice-tracking spectroscopy technique with a scanning tunneling microscope.
We can determine the temperature dependence of the pairing energy gaps, the
electronic excitations in the absence of pairing, and the effect of the local
coupling of electrons to bosonic excitations. Our measurements reveal that the
strength of pairing is determined by the unusual electronic excitations of the
normal state, suggesting that strong electron-electron interactions rather than
low-energy (<0.1 volts) electron-boson interactions are responsible for
superconductivity in the cuprates.
