We have measured the grazing-incidence p-polarized far-infrared reflectivity of Sm2-cursive Greek chiCecursive Greek chiCuO4-δ crystals (Tc = 15 K). C-axis longitudinal-optical phonon features are clearly visible at 430, 570, and 600 cm-1. The phonon frequencies do not shift with temperature, which indicates that the electronic component of the dielectric function remains almost unaltered above the energy scale of 3-4kBTc across the superconducting transition. Below Tc the absorptivity (measured down to 30 cm-1) does not show a signature of a threshold at around 3.5kBTc characteristic of BCS superconductivity. Based on our observations with E(combining right arrow above) ∥ c(combining right arrow above) an upper limit of 30 cm-1 can be placed on the energy of the screened Josephson plasmon for temperatures down to 4 K.
Bibliographical noteFunding Information:
·Research sponsored by Korea Science & Engineering Foundation Grants No. 961-0208-047-2 and No. 96-0702-02-01-3.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering