Optical studies of the a-, b-, and c-axis charge dynamics in YBa2Cu3O6+x
Date
1993Author
Cooper, S. L.Reznik, D.
Kotz, A.
Karlow, M. A.
Liu, R.
Klein, M. V.
Lee, W. C.
Giapintzakis, John
Ginsberg, D. M.
Veal, B. W.
Paulikas, A. P.
Source
Physical Review BVolume
47Pages
8233-8248Google Scholar check
Metadata
Show full item recordAbstract
Optical and Raman-scattering studies of a-, b-, and c-axis YBa2Cu3O6+x between 0.025 and 5.5 eV are presented as a function of doping, and compared to the results of Bi2Sr2CaCu2O8 and La2-xSrxCuO4. Our doping-dependence studies show that the redistribution of spectral weight in the CuO2 planes of YBa2Cu3O6+x differs significantly from that seen in La2-xSrxCuO4. We also find that the redistribution of spectral weight in the cuprates is primarily responsible for the loss of two-magnon Raman-scattering intensity with doping. Finally, we show that bound-carrier contributions comprise a significantly larger fraction of the spectral weight below 1 eV in lower-Tc cuprates such as the 2:1:4 compounds than in higher-Tc cuprates such as YBa2Cu3O6+x and Bi2Sr2CaCu2O8. We suggest that the low-frequency conductivity (<1 eV) in the 2:1:4 compounds is most appropriately described by a two-component picture, while that in YBa2Cu3O6+x and Bi2Sr2CaCu2O8 is adequately described as a single component of strongly interacting carriers. In the metallic phase we find several interesting consequences of a single-component interpretation of the optical data in YBa2Cu3O6+x, such as a linear-in-ω frequency-dependent scattering rate and an increase in the interaction strength with decreased carrier density. Finally, we show that the c-axis optical response in YBa2Cu3O7 (Tc∼90 K) is characterized by a c-axis polarized Raman continuum and a Drude conductivity arising from interbilayer charge transport along the c direction. With decreased doping, the c-axis Drude response decreases dramatically, indicating a decoupling of the CuO2 plane bilayers in YBa2Cu3O6+x. By comparison, the ab-plane optical response is not strongly influenced by interbilayer decoupling, suggesting that the unusual ab-plane charge dynamics in YBa2Cu3O6+x persist in nearly isolated CuO2 plane bilayers. © 1993 The American Physical Society.