Rotons and Ghost Plasmons in Binary and Ternary Ionic Mixtures

ABSTRACT Dynamic properties of two important exanples of binary and ternary ionic mixtures are studied using the self‐consistent version of the method of moments. It is determined that in a mixture the lifetime of the roton branch of the system plasmon‐roton mode is comparable or even shorter than the mode period, that is, that this branch is virtual or strongly decaying. In the ternary mixture this branch's decrement is found to be smaller than its frequency, so that it becomes observable. Conditions are established for the mixture dielectric function to lose its analyticity in the complex frequency upper half‐plane, and the relative contributions to the sum rule of the unique pole located on the positive part of the imaginary axis called the “ghost plasmon” and of other two poles located in the lower half‐plane are found.