Boson modes and Floppy modes in network glasses

Network glasses differ from their crystalline counterparts in a significant way- the presence of an excess of low-frequency vibrations. Here we show that in a covalent\footnote{P. Chen et al. ArXiv 0810.3637} ( As$_{x}$S$_{1-x})$ and in a super-ionic\footnote{D. Novita et al. ArXiv 0808.1154} (AgI$_{(x)}$AgPO$_{3(1-x)})$ glass system, Raman Bose peak scattering strength (I$_{B})$ displays commonalities; in the flexible phase of these systems, I$_{B}$ is found to increase almost linearly as networks become more flexible or their connectivity decreases. Moreover, the rate at which dI$_{B}$/d\textbf{\textit{r}} changes is reminiscent of the variation df/d\textbf{\textit{r}} of the floppy mode count (f) with \textbf{\textit{r }}in rigidity theory. These results suggest that at least in the flexible phase, contributions to the boson peak must result in large part from floppy modes.