Abstract
Optical and Raman-scattering studies of a-, b-, and c-axis between 0.025 and 5.5 eV are presented as a function of doping, and compared to the results of and . Our doping-dependence studies show that the redistribution of spectral weight in the planes of differs significantly from that seen in . 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- cuprates such as the 2:1:4 compounds than in higher- cuprates such as and .
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 and 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 , 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 (∼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 plane bilayers in . By comparison, the ab-plane optical response is not strongly influenced by interbilayer decoupling, suggesting that the unusual ab-plane charge dynamics in persist in nearly isolated plane bilayers.
- Received 13 November 1992
DOI:https://doi.org/10.1103/PhysRevB.47.8233
©1993 American Physical Society