Figure 4. Vibrational amplitudes of normal modes in superlattice S1, for a mass ratio m_B/m_A = 4 with m_A = 0.4 and m_B = 1.6.

The vibrational amplitudes of the eigenvectors, and , in layers A (light) and B (heavy) for all normal modes k, are plotted as functions of the corresponding eigenfrequency ω^k. and are defined in Eq. (6). The repetitions period values are W = 2,4,10,20,40,80 in panels (a–f). The solid line represents the average values and calculated in bins of the form ω^k ± δω^k/2, with δω^k = 0.5. The horizontal dotted lines represent the threshold value , the vertical lines indicate , corresponding to the high frequency edge of g_B(ω).