Interlayer optical response of yttrium barium (copper (cobalt, zinc)) oxide
Karlow, Marvin Anthony
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Permalink
https://hdl.handle.net/2142/19570
Description
Title
Interlayer optical response of yttrium barium (copper (cobalt, zinc)) oxide
Author(s)
Karlow, Marvin Anthony
Issue Date
1996
Doctoral Committee Chair(s)
Wolfe, J.P.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
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.
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