A linear temperature dependence of the specific heat in amorphous solids at very low temperatures is shown to follow from an ionic tunneling model. Moreover, this model predicts both the observed temperature dependence and the magnitude of the thermal conductivity and also explains the anomalous results obtained for the phonon free path by means of stimulated Brillouin scattering.

Tunneling states in amorphous solids

A review is given on the physical properties of electronic charge carriers (electrons, holes) in non-polar and polar liquids. The results are used to explain or discuss certain electric conduction phenomena, which occur when these liquids are subjected to a high electric field strength. Electronic conduction in ultrapure liquids is finding an increasing number of applications.

Electronic Conduction Processes in Dielectric Liquids

Picosecond interferometric technique for study of phonons in the Brillouin frequency range

Ultrasonic Properties of Glasses at Low Temperatures

Publisher Summary This chapter provides evidence that below 1 K, the thermal properties of amorphous insulating solids differ markedly from their crystalline counterparts. The specific heat of amorphous solids is much larger than that of crystals, whereas their thermal conductivity is considerably lower. In pure and defect-free dielectric crystals, both quantities are proportional to T3 at temperatures below 1 K. In amorphous solids, however, the specific heat is almost linear and the thermal conductivity varies almost quadratically with temperature. The tunneling model provides a good phenomenological basis on which various observations are explained. This is the main achievement of the past decade of extensive investigations. The chapter also studies the low temperature anomalies with a much broader perspective and not in isolation, as a problem in it. It is a property of the glassy state in general and a connection should exist between low temperature anomalies and other properties of glasses. It is hoped that such an approach will lead to new ideas and directions and maybe to further surprises.

Chapter 3: Thermal and Elastic Anomalies in Glasses at Low Temperatures

By making use of stimulated Brillouin scattering, hypersonic absorption and velocity measurements in quartz glass were carried out at 24 GHz. Absorption data for longitudinal sound waves are presented below 8°K and velocity data between 4° and 300°K. The hypersonic absorption is observed to decrease strongly on cooling corresponding to a mean free path of the hypersonic phonons larger than 2 mm below 3.5°K. This value exceeds the mean free path calculated from heat conductivity data at 1.5°K for thermal phonons of similar energy by three orders of magnitude. The absorption data are discussed in connection with previous lower‐frequency measurements.

Low‐Temperature Measurement of the Hypersonic Absorption in Fused Quartz by Stimulated Brillouin Scattering

We have measured by a new optical method the hypersonic attenuation in liquid ${\mathrm{He}}^{4}$ at a frequency of about 650 MHz In this high-frequency range absorption data are presented between 12 and 42\ifmmode^\circ\else\textdegree\fi{}K, including the vicinity of the $\ensuremath{\lambda}$ point The results are compared with the previous low-frequency measurements

Hypersonic Absorption in Liquid Helium

Laser-Induced Breakdown in Liquid He 4

We have measured the ultrasonic absorption in crystalline quartz at a frequency of 29 GHz by a new optical method using two consecutive light pulses [1]. This technique enabled us to extend accurate absorption measurements to 200°K, where no other ultrasonic data are available yet.

G. Winterling

Papers

Low‐Temperature Measurement of the Hypersonic Absorption in Fused Quartz by Stimulated Brillouin Scattering

Hypersonic Absorption in Liquid Helium

Laser-Induced Breakdown in Liquid He 4

Optical Determination of the Ultrasonic Absorption in Quartz at 29 GHz