Effect of pair breaking on the optical conductivity in the clean limit

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Abstract
The frequency and temperature dependence of the optical conductivity is quite different in the clean and dirty limits. We have investigated the effect of pair breaking, in the spin-flip model of Abrikosov and Gor’kov for paramagnetic impurities, on the clean-limit ac optical conductivity and compare it with that of the dirty limit. Paramagnetic impurities smear out phonon structure in the density of states and fill in the gap. This behavior is reflected in the low-frequency absorption below 2Δ in the finite-frequency optical conductivity and also in the reduced structure in the Holstein region. Significant differences are predicted between the clean and dirty limits for the optical conductivity.