Pseudo-gap and superconducting condensate energies in the infrared spectra of Pr-doped $\chem{YBa_2Cu_3O_7}

The (a,b)-plane infrared and visible conductivity (30–30000 cm-1) of a 40% praseodymium-substituting yttrium $\chem{YBa_2Cu_3O_7}$ film displays a loss of spectral weight over two separate energy ranges when lowering the temperature. A first loss of spectral weight is present in the range 300–800 cm-1 from room temperature down to 40 K ($T_\ab{c}$ = 35 K). A further distinct spectral weight diminution appears in the superconducting phase at frequencies below 200 cm-1. This diminution can be observed due to the high signal-to-noise ratio allowed by the large area of the thin film. We propose that the lower energy loss of spectral weight reflects the formation and the properties of the superconducting condensate.