How Universal Is the Spectral Density of Tunneling States in Glasses?

Abstract

The low-temperature properties of amorphous solids have attracted the attention of physicists since the beginning of the century. More recently, in 1971, unambiguous evidence was given that below 1 K the thermal properties of amorphous insulating solids differ markedly from those of their crystalline counterparts /1/. In spite of intense experimental and theoretical efforts /2,3/ these “anomalies” can so far only be described on the basis of a phenomenological model /4/. In this so-called “Tunneling Model” (TM) it is assumed that in the amorphous network structural rearrangements are possible even at the lowest temperatures. More specifically: it is assumed that small groups of atoms can tunnel between two different but energetically nearly equivalent sites. Due to the randomness of the amorphous structure, such “Tunneling Systems” (TS) will exhibit a broad distribution of the intrinsic parameters. Thus a rather universal but unspecific interpretation of the low-temperature behaviour of thermal, elastic and dielectric properties of amorphous solids is possible. However, so far the nature of the moving entity is neither known in general nor in specific cases.KeywordsGlass Transition TemperatureMetallic GlassSound WaveAcoustic Surface WaveEnergy SplittingThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.