Dynamically assisted interlayer hopping inYBa2Cu3O6+x

We report evidence from c-axis-polarized Raman scattering and optical-reflectivity measurements that doping-induced and phonon-mediated changes in the O(4)-Cu(1)-O(4) structure influence c-axis charge dynamics in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6+\mathit{x}}$. With increased doping, we observe a rapid increase in the interbilayer hopping rate which we suggest may be caused by the systematic decrease in the Cu(2)-O(4) bond length. Also, c-axis-polarized Raman scattering measurements provide evidence that dynamical modulation of the O(4)-Cu(2) bond length by c-axis phonons contributes to ‘‘assisted’’ interbilayer hopping.