Ultrasonic Study of Percolation Rigidity in Se-Ge Glasses

We have measured the shear elastic modulus C44 of Se1-xGex glasses in the concentration range 0 ≤ x ≤ 0.40, at 4.2 K and at room temperature. A well-resolved threshold is observed at x = 0.36. That result is discussed in the framework of the rigidity percolation. We stress that it contains information on the medium-range order in those glasses: it is not consistent with a continuous random network (which predicts a threshold at x = 0.20) but is consistent with a cluster model.