Low-energy excitations in amorphous polymers

Abstract

In order to investigate low-energy excitations below 10 meV, inelastic neutron-scattering measurements have been carried out on various organic amorphous polymers at 10 and 50 K and three inorganic glasses at 150 and 295 K. It was found that a broad excitation peak is observed for all amorphous materials in the ω range of 1.5–4.0 meV irrespective of different chemical structures. On the other hand, highly crystalline polyethylene with a degree of crystallinity 0.96 shows no such broad peak, indicating that the low-energy excitation is characteristic of amorphous materials. We have employed an asymmetric double-well potential as a common origin for the low-energy excitation in amorphous materials and analyzed the results of amorphous polyisobutylene to confirm validity of this model and alternatively to determine parameters of the potential. Analysis of the temperature dependence of the inelastic-scattering intensity of the low-energy excitation leads to a concept of phonon-assisted tunneling in the asymmetric double-well potential.