Superposition structure of crystal field spectra in High-Tc superconductors:: Overdoped regime

Experiments on inelastic scattering of neutrons show that the crystal field spectra for high-T-c superconductors R1-yCayBa2Cu3Ox approximate to 7 (R = Ho, Er; 0 < y < 0.25) have two spectral components associated with optimally doped and overdoped clusters, respectively. An increase in the calcium concentration does not affect the local density of charge carriers in clusters, but changes the concentration of clusters themselves and, hence, the spectral weights of the spectral components. In light of such a "two-phase" pattern observed earlier for cuprate-based superconductors with a doping level below optimal, an increase in the charge carrier concentration leads to a smooth transition (crossover) from the underdoped regime to the overdoped one. The obtained results show, however, that these two regions of the phase diagram differ qualitatively in the form of charge distribution in CuO2 planes responsible for superconductivity. (C) 2002 MAIK "Nauka/Interperiodica".