In order to understand the low-energy vibrational excitations common to amorphous solids, we have studied their evolution in ion-implanted crystalline silicon by measuring internal friction and heat conduction. The spectral density of these low-energy excitations evolves with increasing dose exactly towards that observed in the amorphous phase. More importantly, this evolution is unrelated to that of the amorphicity. We conclude that the defects in the crystal should be used to model the excitations in the amorphous silicon, rather than the amorphous structure itself.

• Received 29 June 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.3171