Infrared studies of the normal and superconducting states of Y₁Ba₂Cu₃O₇

We describe infrared measurements of the a-b-plane response of Y1Ba2Cu3O7 crystals with Tc ≈ 92 K. We observe a self-energy structure at a characteristic energy of 500 cm-1 (8kTc), the appearance of which coincides with the transition to the superconducting state. The nature of this self-energy anomaly is consistent with its identification as a nodeless a-b-plane energy gap at 2Δ ≈ 8kTc. On the basis of temperature-dependent measurements above Tc, we suggest that the normal state can be primarily characterized by a carrier band with an enhanced low-frequency mass and a frequency-dependent scattering rate. Our data indicate that these arise from coupling to an excitation spectrum with characteristic frequencies up to ω-c$/ approximately 700 cm-1 and a coupling strength of λ ≈ 2-3.