Determination of the number of Raman active modes of the Bi2Sr2CaCu2O8 superconductor

Abstract

Raman spectroscopy has been extensively used in the study of the structural and electronic properties of solids. In the field of superconductors, the energy range of the lattice vibrations are of the same order as the energy gap. Thus, Raman scattering has been used to study the characteristics of the energy gap of superconductors. At the same time the technique has been used to study the structure of superconductors. The spectra reveal not only the energy ofthe lattice vibrations, but also the strength of bonding between atoms. For superconductors, in particular the Bi-2212 superconductor, the assignment of vibrational modes must be made correctly in order to be able to use the Raman technique as a tool to fully understand the phenomenon of superconductivity.
The exact structure of the Bi-2212 superconductor still remains unresolved. Although the tetragonal structure has been consideied in this study, the structure has also been classified under the Bbmb and Amaa orthorhombic space groups. Deviations from the tetragonal structure have been attributed to the incommensurate modulation of the Bi-2212 lattice and displacements of atoms from the unit cell resulting in an orthorhombic structure.
While other studies have based the interpretation of the Raman spectra on the tetragonal structure, the explicit calculation of the number of Raman active modes have not been shown. In this study, we present the calculations used in determining the number of Raman active modes using the I4/mmm structure.