Collective phenomena in multi - band superconducting systems doped with non magnetic impurity

Abstract

The overlapping of energy bands on the Fermi surface changes the properties of multi – band superconductors as qualitatively as well quantitatively. Here we investigate the appearance of collective oscillations caused by phase fluctuations of order parameters from different bands. Namely, how non- magnetic chaotic distributed impurity influences on the collective oscillations in two – band superconductors. Two – particle Green function is considered and the system for vertex functions averaged on chaotic distributed impurity are obtained using the Hamiltonian of two – band superconductors. Necessary values to determine the frequency of collective oscillations ω are calculated in linear approximation after the impurity concentration. The equation for ω is obtained and its solutions are found. It is shown that in this doped system an exciton – like frequency of collective oscillations could arise. At low impurity concentration the damping of collective oscillations is absent.