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Abstract:
We have measured the optical absorption spectrum of YBa2Cu3O7-delta
crystalline thin films and powders in the range 2000 to 10000 cm-1. A
broad absorption band near 5500 cm-1 (0.7 eV) is observed, which has the
same absorption profile in both cases. Our work on thin-film samples
shows that the excitation causing this absorption is polarized in the ab
plane. Further work on doped powder samples provides evidence that the
excitation is localized in the CuO2 planes of the structure, which are
known to be the principal carriers of the superconductivity. Studies of
the temperature dependence of the absorption have revealed that the peak
intensity undergoes a transition at the superconducting transition
temperature, providing firm evidence that the excitation is coupled to
the superconducting order parameter.
