Cu-0 Superconductors: Through a Lens, but Darkly
The shock of superconducting transition temperatures (Tc’s) greater than 25 K in Cu-O based compounds1 has loosed a tidal wave of research. We have involved ourselves in a study of the optical properties of these materials, with particular emphasis on La2-xSrxCuO4 compounds. Recently we reported 2 reflectivity, R, spectra of La2-xSrxCuO4 for x = 0 and 0.175, and of Ba2YCu3O9-δ (δ~2.1) over a broad range of photon energy. The most striking observation was the profound deviation from the expected Drude-like R in the metallic compounds. Fitting R required that ∈ (ω) be dominated by a transition at energy 0.45 eV in La1.825Sr175CuO4 and 0.65 eV in Ba2YCu3O9-δ. From our fit we determined that the integrated oscillator strength in the 0.45 eV feature in La1.825Sr0.175CuO4 corresponded to a value of Neff m/m* of 2.5xl021cm-3. This density agrees well with the density of positive carriers (assuming one hole per Sr atom) of 1.9x 1021cm-3. Similar conclusions for La1.825Sr0.175CuO4 were reached by Herr et al.3 based upon Kramers-Kronig (KK) analysis of their R data.
Unable to display preview. Download preview PDF.
- 2.J. Orenstein, G. A. Thomas, D. H. Rapkine, C. B. Bethea, B. F. Levine, R. J. Cava, E. A. Rietman, and D. W. Johnson, Phys. Rev. B, in press.Google Scholar
- 3.S. L. Herr, K. Kamaras, C. D. Porter, M. G. Doss, D. B. Tanner, D. A. Bonn, J. E. Greedan, C. V. Stager and T. Timusk, Phys. Rev. B, in press; D. A. Bonn, J. E. Greedan, C. V. Stager, T. Timusk, M. Doss, S. Herr, K. Kamaras, C. Porter, D. B. Tanner, J. M. Tarascon, W. R. McICinnon and L. H. Greene, Phys. Rev. B, in press.Google Scholar
- 7.P. W. Anderson, Science 235, 1196 (1987). S. A. Kivelson, D. S. Rokhsar, and J. P. Sethna, to be submitted.Google Scholar