The low-temperature thermal properties of amorphous arsenic

Abstract

Below 1 K the heat capacity C(T) of bulk amorphous As is proportional to the cube of the absolute temperature T, in marked contrast to the behaviour of other amorphous solids. Above 1 KC(T)/T³ increases rapidly to a maximum at about 5 K, decreasing more gradually at higher temperatures, in a way that resembles other amorphous solids. The thermal conductivity k varies as T³ below 0.3 K, shows a plateau centred at about 5 K, and increases again above 10 K. The T³ variation below 0.3 K is shown to be a result of phonon scattering by small holes in the sample, giving a constant phonon mean free path of 25 μm.

The temperature dependence and magnitude of k are discussed in terms of two different theories, neither of which is completely satisfactory. The effects of dispersion are included with the help of parameters derived from the heat capacity, but this is shown to have little effect on the strength of scattering needed to explain. the plateau. Finally, it is suggested that phonon-phonon scattering may account for the temperature variation of k in amorphous solids above 1 K.