PHONON SPECTRA OF HIGH TEMPERATURE SUPERCONDUCTOR Bi2Sr2Ca2Cu3O10 : THEORY AND EXPERIMENT*

Since the discovery of the high Tc superconductivity by Bednorz and Muller, several workers around the world have studied several systems to reach a really high Tc superconductor. As the strong electron-phonon coupling may be one of the possible origins of the high Tc, a knowledge about the phonon in these materials is essential. In order to investigate phonon spectra, Raman and infrared spectra of these systems have been studied.But there is a little information available in the literature for complete Raman and infrared absorption spectra. Infrared is of little use for characterization purposes but important for fundamental studies provided single crystals are used. Due to the nature of the superconductivity materials, it is not possible to obtain all the phonon frequencies experimentally through Raman and infrared spectra. Hence a theoretical evaluation of phonon frequencies of high temperature superconductors assumes importance. The Fourier transform Raman spectra of Bi2Sr2Ca2Cu3O10 have also been recorded in the solid phase in the range of 700 to 100 cm using Bruker IFS 66V FTIR Spectrometer with FRA R06 Raman module for the experimental confirmation of the present assignment. Due to strong covalent bonding nature in high temperature superconductors, a normal coordinate analysis using Wilson’s FG matrix is applied here to evaluate phonons frequencies of Bi2Sr2Ca2Cu3O10. The normal coordinate analysis of optically active lattice vibrations will be useful for the theoretical interpretation of vibrational spectrum at the center of Brillouin zone for Bi2Sr2Ca2Cu3O10 high Tc superconductor. Calculations of lattice dynamics is also performed using the modified three body force shell model (TSM). The present approach leads to a better understanding of phonons frequency of high Tc superconductor Bi2Sr2Ca2Cu3O10. This calculation yields the zone center phonons modes and potential energy distribution helps to identify the pure and mixed frequencies. This gives further support in understanding the phonons spectra of the high temperature superconductors. Hence, the present approach is useful not only to obtain all the phonons frequencies of high temperature superconductor Bi2Sr2Ca2Cu3O10 reasonably but also to characterize it.