  Temperature and composition dependences of high-energy longitudinal optical
(LO) phonons in YBa2Cu3O{6+x}, studied by inelastic neutron scattering
measurements, provide clear evidence for temperature dependent spatial
inhomogeneity of doped charges. The measurements indicate that charge doping
increases the volume fraction of the charged regions, while the local charge
density remains unchanged. For the optimally doped sample the charge
distribution changes sharply near the superconducting transition temperature,
with stronger charge inhomogeneity below Tc. The remarkable magnitude of the
phonon response to charge suggests strong involvement of phonons in charge
dynamics.
