NEUTRON-SCATTERING BY PHONONS IN QUASI-CRYSTALS

Using the spectral moments method, the authors studied the inelastic scattering by phonons in very long Fibonacci chains. The results show that the pseudo-acoustic dispersion curves can be associated with Bragg peaks. The intensity of the acoustic phonon lines is proportional to the intensity of the corresponding Bragg peak. A study of disordered Fibonacci chains shows that the intensity of the phonon lines decreases strongly with increasing disorder. These results could explain the difficulties encountered in measurements of the acoustic modes in quasi-crystals.