paper

In-plane optical conductivity of La $_{2 - x}$ Sr $_{x}$ CuO $_{4}$ : Reduced superconducting condensate and residual Drude-like response

arXiv:cond-mat/0401447 · doi:10.1103/PhysRevB.71.094508

Abstract

Temperature dependences of the optical spectra of La $_{2 - x}$ Sr $_{x}$ CuO $_{4}$ with $x$ =0.12 and 0.15 were carefully examined for a polarization parallel to the CuO $_{2}$ -plane over a wide frequency range down to 8 cm $^{- 1}$ . Selection of well-characterized crystals enabled us to measure purely in-plane polarized spectra without any additional peak. The weight of superconducting (SC) condensate estimated from the missing area in $I ¨ _{1} (I ¨ $ ) well agrees with the estimate from the slope of $I ¨ _{2} (I ¨ $ ) vs 1/ $I ¨ $ plot, showing no evidence that the Ferrell-Glover-Tinkham sum-rule is violated in the optical spectrum. We demonstrate that the optically estimated SC condensate is much smaller than the value obtained from the $I^¼$ SR measurement of magnetic penetration depth. We also find an anomalous increase of conductivity in sub-millimeter region towards $I ¨ $ =0 below $T_{c}$ , which suggests the microscopic inhomogeneity in the superconducting state. Both observations are discussed in relation with the inhomogeneous electronic state that might be inherent to high- $T_{c}$ cuprates.

10 pages, 6 figures

In-plane optical conductivity of La2−x​Srx​CuO4​: Reduced superconducting condensate and residual Drude-like response

Abstract

In-plane optical conductivity of La $_{2 - x}$ Sr $_{x}$ CuO $_{4}$ : Reduced superconducting condensate and residual Drude-like response