Abstract
Recent development is reviewed of experimental and theoretical studies on low-temperature heat capacity of solid, from the viewpoint of the Anderson's theory. Besides the two-level-systems assumed by Anderson et al., “additional” low-energy excitations have recently been discovered for a number of amorphous solids. Computer simulation supported existence of such excitations. They were also explained by “soft-potential” theory. Anomalous temperature dependences of heat capacity or sound velocity have also been recognized recently in such crystalline solids, as solid electrolyte, high-Tc superconductors and pure metals, etc. The behavior is similar to those of amorphous solids and can be explained by the Anderson's theory.
