Infrared studies of the normal and superconducting states of Y1Ba2Cu3O7

We describe infrared measurements of the a-b-plane response of Y
1
Ba
2
Cu
3
O
7
crystals with T
c
≃ 92 K. We observe a self-energy structure at a characteristic energy of 500 cm
⁻¹
(8kT
c
), 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 ≃ 8kT
c
. On the basis of temperature-dependent measurements above T
c
, 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
∼ 700 cm
⁻¹
and a coupling strength of λ ≃ 2–3.