Charge redistribution in YBa₂Cu₃O_7-d probed by Raman spectroscopy: CuO₂-plane phonon as a probe of carrier dynamics in the CuO₂ plane

Yttrium barium copper oxide system, which undergoes a metal-to-insulator transition under variation of carrier concentration, was investigated using Raman spectroscopy. The intensity of CuO₂-plane phonon modes decreased as the system approached the metal-to-insulator phase boundary and it scaled with the inverse of the hole concentration within the CuO₂ conducting planes. The CuO₂-plane mode intensity and transition temperature for the oxides was found to be correlated. It was found that a simple and useful probe for metal-to-insulator transition and carrier dynamics in the CuO₂ plane for substituted materials was provided by this correlation and the CuO₂-plane mode intensity.