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Abstract
The FIR transmission of an YBa2Cu3O7-δ film 1000 Å thick deposited on an MgO plate has been studied from 20 cm−1 to 4000 cm−1 at T = 300 K, and at 120 K, 80 K and 7 K. i) The spectra for the normal state are well fitted if a mid-IR oscillator of high strength and high damping is added to the simplest Drude model. ii) The spectra for the superconductive state do not show significant variations of transmission vs. temperature for ω > 120 cm−1, which should be in agreement with a weak BCS coupling 2Δ = 3.5 kTc . iii) The FIR transmission at 7 K for ω = 20 cm−1 is not zero (around 1%) and seems to confirm that the low-temperature perovskite is made of two phases: a superconducting, and a normal one, the proportion of the first one increasing when the film temperature is decreased.