2005/05/11 by J. Hwang, J. Yang, T. Timusk +5 · 1 citation
Physics and Astronomy · #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.73.014508
published as Phys. Rev. B 73, 014508 (2006). · 13 pages 16 figures
arxiv created 2005/05/11 · arxiv updated 2009/12/01
The a-axis optical properties of a detwinned single crystal of YBa2Cu3O6.50 in the ortho II phase (Ortho II Y123, Tc= 59 K) were determined from reflectance data over a wide frequency range (70 - 42 000 cm-1) for nine temperature values between 28 and 295 K. Above 200 K the spectra are dominated by a broad background of scattering that extends to 1 eV. Below 200 K a shoulder in the reflectance appears and signals the onset of scattering at 400 cm-1. In this temperature range we also observe a peak in the optical conductivity at 177 cm-1. Below 59 K, the superconducting transition temperature, the spectra change dramatically with the appearance of the superconducting condensate. Its spectral weight is consistent, to within experimental error, with the Ferrell-Glover-Tinkham (FGT) sum rule. We also compare our data with magnetic neutron scattering on samples from the same source that show a strong resonance at 31 meV. We find that the scattering rates can be modeled as the combined effect of the neutron resonance and a bosonic background in the presence of a density of states with a pseudogap. The model shows that the decreasing amplitude of the neutron resonance with temperature is compensated for by an increasing of the bosonic background yielding a net temperature independent scattering rate at high frequencies. This is in agreement with the experiments.