An optical "pseudogap" is often assumed to open at low T in the "anomalous Drude" absorption, which models the optical conductivity σ(ω)∝ω-1 of high-Tc superconductors by a linewidth Γ ≈ 103 cm-1 varying with ω. In the σ(ω) of Bi2Sr2CuO6 measured down to 10 cm-1, we have resolved, instead, two components separated by a deep minimum: (i) a normal Drude term with Γ = 35 cm-1 at 30 K, in very good agreement with transport data; (ii) a strong band peaked in the far infrared (FIR), likely due to bound charges, whose tail exhibits the ω-1 dependence. As the FIR peak softens for T→0, it opens a pseudogaplike depression in σ(ω) accordingly to ordinary sum rules.
Evidence of two species of carriers from the far-infrared reflectivity of Bi2SR2CuO6 / Lupi, Stefano; Calvani, Paolo; Capizzi, Mario; P., Roy. - In: PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS. - ISSN 1098-0121. - STAMPA. - 62:18(2000), pp. 12418-12421. [10.1103/physrevb.62.12418]