Method of distinction of pure d-wave state from the mixed state in HTSC

Direct observation of the collective modes in unconventional superconductors (USC) by microwave impedance technique experiments has made the study of the collective excitations in these systems very important. One remaining question is the exact form of the order parameter of unconventional superconductors. Extended s-wave pairing, mixture of s- and d-states, as well as of different d-wave states are among possibilities. We have considered the mixtures of dx2-y2 and dxy states in high temperature superconductors (HTSC) and have, for the first time, derived the full set of equations for the collective mode spectrum in the mixed d-wave state with an arbitrary admixture of dxy state. The results we have obtained will allow us to calculate the whole collective mode spectrum, which may then be used for interpretation of sound attenuation and microwave absorption data as well as for identification of the type of pairing and order parameter in unconventional superconductors. In particular, this will allow one to estimate the extent of admixture of dxy state in the possible mixed state.