Ab-plane optical properties of Tl2Ba2CuO6+ delta.

Abstract

We report on absolute ab-plane reflectivity measurements of the single-layer high-${\mathit{T}}_{\mathit{c}}$ superconductor ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CuO}}_{6+\mathrm{\ensuremath{\delta}}}$ in both the normal and superconducting states. The reflectivity has been measured from 40 to 40000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and the optical conductivity has been calculated from Kramers-Kronig analysis. The unusual form of the low-frequency reflectivity leads to an intense low-frequency feature in the optical conductivity. In the superconducting state, the spectral weight is strongly suppressed at frequencies below \ensuremath{\sim}800 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ due to the formation of a superfluid fraction. The value of the London penetration depth has been estimated to be 2400\ifmmode\pm\else\textpm\fi{}200 \AA{}, larger than that from muon-spin-resonance (\ensuremath{\mu}SR) experiments.