The Influence of Two-Level States on the Thermal Conductivity of Amorphous Materials

The thermal properties of almost all amorphous materials at low temperatures exhibit certain very general features. Below about 1 K the specific heat has a contribution linear in the temperature T in addition to the ordinary phonon (Debye) T3 term, and the thermal conductivity in this region varies as Tn where n is usually about 1.8. At slightly higher temperatures, usually between 5 and 10 K, the thermal conductivity passes through a plateau-like region in which its value is almost constant, before it starts to increase again at higher temperatures.