Optical cooper pair breaking spectroscopy of cuprate superconductors

The photon energy dependence of the optical Cooper pair breaking rate (CPBR) is studied for compressibly strained ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}$ (LSCO) films and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{2.92}{\mathrm{Zn}}_{0.08}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YBCZO) thin films, and compared to that in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (YBCO). Unlike YBCO, the CPBR for LSCO does not show an obvious photon energy dependence. In YBCZO, the CPBR shows a strong energy dependence similar to YBCO, but with a redshift in the peak position. Analysis of these results strongly favors a physical picture based on electronic phase separation in high-${T}_{c}$ superconductivity.