Vibrational melting and its possible relevance to amorphous silicon

Abstract

The conventional melting of “simple” substances involves configurational excitation from multi-dimensional potential energy basins surrounding crystalline structures to those surrounding amorphous structures. Vibrational anharmonicity changes relatively little in extent across such transitions. Motivated by observations of a sharp melting point for solid amorphous silicon well below that of the crystal, another possibility is proposed. This requires cooperative softening of vibrational modes with increasing mean amplitude. An exactly solvable model for this type of strong anharmonicity demonstrates that it can produce a first-order “intrabasin melting”, or a critical point with a symmetric heat capacity divergence.