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Title:Interlayer optical response of yttrium barium (copper (cobalt, zinc)) oxide
Author(s):Karlow, Marvin Anthony
Doctoral Committee Chair(s):Wolfe, J.P.
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Physics, Condensed Matter
Abstract:We report optical reflectance and spectroscopic ellipsometry measurements of the in- and out-of-plane dielectric responses of chain substituted $\rm YBa\sb2Cu\sb3O\sb{6 + x}$ and $\rm YBa\sb2(Cu\sb{1 - y}Co\sb{y})\sb3O\sb{6 + x}$ and of plane substituted $\rm YBa\sb2(Cu\sb{1 - y}Zn\sb{y})\sb3O\sb{6 + x}.$ A dramatic decrease in the low-frequency c-axis optical conductivity, $\sigma\sb{\rm c}(\omega),$ is observed with either O reduction or Co substitution, suggesting that structural changes in the Cu(1)-O(4)-Cu(2) complex between the CuO$\sb2$ bilayers dominate the doping dependence of interlayer coupling in $\rm YBa\sb2(Cu\sb{1 - y}M\sb{y})\sb3O\sb{6 + x}$ (M = Co, Zn). The slight decrease in $\sigma\sb{\rm c}(\omega)$ observed with Zn substitution suggests that the charge dynamics in the CuO$\sb2$ planes play at best a minor role in regulating interlayer hopping. We find that the electronic component of the c-axis optical conductivity in $\rm YBa\sb2Cu\sb3O\sb{6 + x}$ is roughly constant below 800 cm$\sp{-1}$, and is well fit over the frequency range 800 cm$\rm\sp{-1} \le\omega\le3200\ cm\sp{-1}$ by $\sigma\sb{\rm c}(\omega)\propto\omega\sp\gamma\ (0 \le\gamma<1.2),$ for all oxygen concentrations $\rm 0.26 \le x \le 0.93.$ The consequences of these results for theories of c-axis transport in the cuprates are discussed. Absorption bands near 0.95 and 2.7 eV in $\sigma\sb{\rm c}(\omega)$ are assigned to plane-to-chain antibonding band transitions, while the c-axis polarized 1.7 eV absorption is attributed to charge transfer transitions between O and Cu atoms in adjacent CuO$\sb2$ planes of a bilayer. We consider the proposed connection between the pseudogap in the c-axis optical conductivity, and the deviations from linearity in the in- and out-of-plane resistivity, and discuss the possibility that either interlayer dynamic disorder or low-q spin scattering may account for these unusual features. Notably, c-axis polarized electronic Raman scattering measurements are discussed that provide evidence for a specific incoherent contribution to $\sigma\sb{c}(\omega)$ resulting from optical phonon assisted interlayer hopping.
Issue Date:1996
Rights Information:Copyright 1996 Karlow, Marvin Anthony
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9702554
OCLC Identifier:(UMI)AAI9702554

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