Viscoelastic anomaly accompanying anti-crossing behaviour in liquid As₂Se₃

We investigate the dynamic structure factor of the melt of the well known glass former, As₂Se₃, using inelastic x-ray scattering for temperatures, T, K and momentum transfers Q from nm⁻¹. An anomaly was observed at Q  =  2.7 nm⁻¹ ( K) with, in the context of a simple model, both an abrupt change in frequency and an increased linewidth reminiscent of an anti-crossing in a solid. Comparison with structural information from reverse Monte Carlo modeling of x-ray diffraction data allows us to associate the disappearance of the anomaly at higher temperatures with a drop in the number of mechanical constraints per atom, n _mc, to reminiscent of the threshold applicable for glass formation in rigidity theory. It is inferred that the surprising jump in the dispersion in the liquid may be correlated with a stiffness transition in a network glass. (letter)