The field of viscous liquid and glassy solid dynamics is reviewed by a process of posing the key questions that need to be answered, and then providing the best answers available to the authors and their advisors at this time. The subject is divided into four parts, three of them dealing with behavior in different domains of temperature with respect to the glass transition temperature, Tg , and a fourth dealing with ‘‘short time processes.’’ The first part tackles the high temperature regime T.Tg ,i n which the system is ergodic and the evolution of the viscous liquid toward the condition at Tg is in focus. The second part deals with the regime T;Tg , where the system is nonergodic except for very long annealing times, hence has time-dependent properties ~aging and annealing!. The third part discusses behavior when the system is completely frozen with respect to the primary relaxation process but in which secondary processes, particularly those responsible for ‘‘superionic’’ conductivity, and dopart mobility in amorphous silicon, remain active. In the fourth part we focus on the behavior of the system at the crossover between the low frequency vibrational components of the molecular motion and its high frequency relaxational components, paying particular attention to very recent developments in the short time dielectric response and the high Q mechanical response. © 2000 American Institute of Physics.@S0021-8979~00!02213-1#

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1065&context=mse_pubs

Relaxation in glassforming liquids and amorphous solids

Recent research and development has been incredibly successful at advancing the capabilities for vacuum electronic device (VED) sources of powerful terahertz (THz) and near-THz coherent radiation, both CW or average and pulsed. Currently, the VED source portfolio covers over 12 orders of magnitude in power (mW-to-GW) and two orders of magnitude in frequency (from ; 10 THz). Further advances are still possible and anticipated. They will be enabled by improved understanding of fundamental beam-wave interactions, electromagnetic mode competition and mode control, along with research and development of new materials, fabrication methods, cathodes, electron beam alignment and focusing, magnet technologies, THz metrology and advanced, broadband output radiation coupling techniques.

Vacuum Electronic High Power Terahertz Sources

Polyatomic molecules can exist as nuclear spin isomers. For example, the ortho and para hydrogen spin isomers are characterized by different values of specific heat, boiling point, heat of vapor formation, and so forth ([1][1]). Hydrogen has been the only substance whose spin modifications are well

/pdf/separation-of-water-into-its-ortho-and-para-isomers-kou6rj7ep4.pdf

Separation of water into its ortho and para isomers.

Microwave dielectric properties and far infrared reflectivity spectra were investigated in the (Zr0.8Sn0.2)TiO4 ceramics with 1 mol% Sb2O5, Sb2O3 and Nd2O3, respectively. Dielectric constant was not significantly changed, while the unloaded Q value was affected with additives. The unloaded Q of the pure (Zr0.8Sn0.2)TiO4 specimens was higher than that of the specimens with Sb2O3 and/or Nd2O3, but lower than that of the specimens with Sb2O5. The high unloaded Q value of 6600 at 7 GHz was obtained for the specimens with 1 mol% Sb2O5 due to elimination of oxygen vacancies. The effects of additives on the intrinsic microwave losses of the specimens were investigated by the infrared reflectivity spectra from 50 to 4000 cm-1, which were evaluated using the Kramers-Kronig analysis and classical oscillator model. The relative tendency of microwave dielectric properties calculated from the reflectivity data was in good agreement with the results by the Hakki and Coleman's method.

https://iopscience.iop.org/article/10.1143/JJAP.37.5367/pdf

Microwave dielectric properties and far infrared reflectivity spectra of the (zr0.8sn0.2)tio4 ceramics with additives

The electrodynamics of topological insulators (TIs) is described by modified Maxwell’s equations, which contain additional terms that couple an electric field to a magnetization and a magnetic field to a polarization of the medium, such that the coupling coefficient is quantized in odd multiples of α/4π per surface. Here we report on the observation of this so-called topological magnetoelectric effect. We use monochromatic terahertz (THz) spectroscopy of TI structures equipped with a semitransparent gate to selectively address surface states. In high external magnetic fields, we observe a universal Faraday rotation angle equal to the fine structure constant α=e2/2
 hc (in SI units) when a linearly polarized THz radiation of a certain frequency passes through the two surfaces of a strained HgTe 3D TI. These experiments give insight into axion electrodynamics of TIs and may potentially be used for a metrological definition of the three basic physical constants. The electrodynamics of topological insulators has been predicted to show a new magnetoelectric term, but this hasn’t been observed. Here, Dziomet al. observe a universal Faraday rotation angle equal to the fine structure constant, evidencing the so-called topological magnetoelectric effect.

/pdf/observation-of-the-universal-magnetoelectric-effect-in-a-3d-240f3xmgu5.pdf

Observation of the universal magnetoelectric effect in a 3D topological insulator

Dielectric measurements in the submillimeter wavelength region

Coherent source submillimeter wave spectroscopy

The complex permittivity spectra of the alumina A12O3, mixed perovskites CaTiO3-La(Mg1/2Ti1/2)O3, (Zr,Sn)TiO4 and BaO. 4TiO2. Nd2-xSm x O3 ceramics have been determined employing various techniques in the 1010–1014 Hz range. In samples with minimized loss its origin is lattice phonon absorption in the whole spectral range. In not optimized samples the microwave losses are appreciably higher (probably due to localized hopping of charged defects) but submillimetre losses remain unaffected. Extrapolating the submillimetre loss using the proportionality e″“(v)x v allows one to estimate the lower limit of microwave loss achievable by any processing.

Dielectric spectra of some ceramics for microwave applications in the range of 1010–1014 Hz

Progress in submillimeter spectroscopy of solid state

The dielectric dispersion associated with the ferroelectric phase transition in Li 2 Ge 7 O 15 has been measured in the paraelectric phase by means of a backward-wave oscillator spectrometer in the frequency region 8-24 cm -1 . A temperature dependent resonant mode was found, which corresponds to the soft mode previously observed in the ferroelectric phase by Raman scattering. This mode has a very small oscillator strength and its contribution to the dielectric constant does not exceed 0.1 even in the vicinity of the transition point. A relaxational mode with the characteristic frequency of about 0.03 cm -1 is required for consistently explaining the reported dielectric anomaly.

G.V. Kozlov

Papers

Dielectric measurements in the submillimeter wavelength region

Coherent source submillimeter wave spectroscopy

Dielectric spectra of some ceramics for microwave applications in the range of 1010–1014 Hz

Progress in submillimeter spectroscopy of solid state

Observation of the Soft Polar Mode in the Paraelectric Phase of Li 2 Ge 7 O 15