We analyze the infrared reflectivity of La1.85Sr0.15CuO4 single crystals with E parallel to the c-axis. The plasma edge at around 6 meV (50 cm-1), which occurs only for T < Tc, is due to Cooper-pair tunneling. This low value of the plasma edge is shown to be consistent with the c-axis plasma frequency obtained from LDA band structure calculations (> 0.1 eV) if we take into account that the single-particle charge transport along the c-axis is strongly incoherent in the normal state, and remains so in the superconducting state. From a comparison of the optical conductivity with model calculations based on s- and d-wave weak-coupling theory in the dirty limit, we find no evidence for a reduction of the c-axis quasi-particle scattering rate below Tc. The c-axis scattering rate, the normal-state c-axis plasma frequency, and Tc obey hγ > hνp ≫ 3.5κBTc, which is exactly opposite to the clean limit.
Bibliographical noteFunding Information:
We gratefully acknowledge stimulating discussions with P. W. Anderson during the preparation of this manuscript. This investigation was supported by the Netherlands Foundation for Fundamental Research on Matter (FOM) with financial aid from the Neder-landse Organisatie voor Wetenschappelijk Onderzoek (NWO).
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering