Optical properties and acoustic phonon dynamics of Bi₂Sr₂CaCu₂O₈₊δ crystals

Abstract

In this work, the optical properties and acoustic phonon behaviour of several Bi₂Sr₂CaCu₂O₈₊δ0 (Bi-2212) superconducting crystals were investigated. Reflectance imaging on Bi-2212 crystals was first performed and along with Kramers-Kronig analysis, allowed for the extraction of the refractive index, extinction coefficient and both parts of the complex dielectric function. With these measured reflectances, a newly refined optical contrast method was presented and used in an attempt to obtain a secondary estimate of the refractive index and extinction coefficient of these crystals. Brillouin light scattering experiments were performed on Bi-2212 crystals at room temperature where six different acoustic modes were observed; the Rayleigh surface mode, two quasi-transverse bulk modes, the quasi-longitudinal bulk mode and two currently unknown modes. Using the peak frequency shifts and widths of the quasi-transverse and surface modes, the refractive index and extinction coefficient were extracted and used to calculate both parts of the complex dielectric function which were then compared to results found by reflectance analysis. The refractive index was then used to calculate the velocities of the three bulk modes and two unknown modes for angles ranging from approximately 3ᴼ to 21ᴼ from the [001] direction.