Quasi two-dimensionality of the phonon subsystem in bismuth superconductors

To study the vibrational spectra of multi-component bismuth superconductors, a comparative analysis method is proposed and used for a number of compounds formed by a succesive addition of new layers. It is found that with the transition from one compound to another the frequencies of bulk phonons due to the layer vibrations change slightly, i.e. determined predominantly by the intralayer parameters, allowing to conclude about the quasi 2D character of the phonon subsystem in bismuth superconductors