Neutron spectroscopic studies of the crystal field in : evidence for a percolative metal-insulator transition

Crystal-field (CF) transitions within the ground-state J-multiplet of in have been observed with inelastic neutron scattering. From the CF parameters a negative charge enhancement in the planes is derived upon doping with cerium. Two electronically inequivalent sites in the Ce-doped samples are identified corresponding to undoped and doped micro-regions. Furthermore, the volume fraction of the two components is determined, and it is shown that the metal-insulator transition can be explained by the formation of a two-dimensional percolative network of the doped micro-regions.