Abstract

Very recent spectroscopic data of YBa₂Cu₃O_7-δ (YBCO) films suggest that oxygen doping dramatically changes the electronic structure of the CuO₂ plane.¹,² The femtosecond 2-eV-pump/white-light-continuum-probe experiments performed at room temperature on YBCO thin films with various oxygen contents showed that in fully oxygenated YBCO samples (T_c ~90 K) the transient optical reflectivity (AR/R) signal remains positive for all probe energies from 1.91 eV to 2.25 eV, whereas the response of oxygen-poor films (T_c ~0 K) is negative down to 1.46 eV.3 The lack of sign reversal for AR/R in either type of YBCO suggests that the results for the oxygen-rich samples could be interpreted as intraband free-carrier absorption, while the response in the oxygen-poor YBCO resulted from the saturation of interband absorption across the charge-transfer gap.

© 1994 Optical Society of America