Far-infrared c-axis response of La1.87Sr0.13CuO4 determined by ellipsometry.

摘要: We have measured the $c$-axis optical response of a large, high-quality single crystal ${\mathrm{La}}_{1.87}$${\mathrm{Sr}}_{0.13}$Cu${\mathrm{O}}_{4}$ between 30 and 700 ${\mathrm{cm}}^{\ensuremath{-}1}$ in 10-300 K temperature range with far-infrared Fourier ellipsometer. Since ellipsometry provides both amplitude phase information, we directly obtain complex dielectric function, thereby avoiding errors introduced by Kramers-Kronig transformation or reference determination. A purely algebraic treatment our data within two-fluid Gorter-Casimir model reveals no indication reduction normal carrier scattering rate $\ensuremath{\Gamma}$ below ${T}_{c}$. $\ensuremath{\Gamma}\ensuremath{\approx}130\ifmmode\pm\else\textpm\fi{}70$ plasma frequency for superconducting carriers ${\ensuremath{\omega}}_{\mathrm{ps}}\ensuremath{\approx}260\ifmmode\pm\else\textpm\fi{}40$ ${\mathrm{cm}}^{\ensuremath{-}1}$. Thus, assuming weak-coupling BCS gap ($3.5{k}_{B}{T}_{c}\ensuremath{\approx}77$ ${\mathrm{cm}}^{\ensuremath{-}1}$, ${T}_{c}=31.5$ K) conclude that can neither be modeled clean nor dirty limit.