Abstract
We observed two photoinduced infrared excitations in insulating Y1Ba2Cu3O6 + y, similar to La2CuO4 and Nd2CuO4 systems. Our results indicate that the lower-energy excitation does not have the same physical origin as the higher-energy excitation. Remarkably, the lower-energy excitation peak position abruptly redshifts at a well-defined onset temperature, coinciding with the Tc of the corresponding superconductor. Furthermore, the amount of the redshift scales with Tc.