Image by leungchopan/Shutterstock

A research team led by University of Tsukuba has developed a continuum model that explains why glass loses transparency to terahertz (THz) radiation above a characteristic frequency. This model links the terahertz dielectric response of glass to its internal mechanical properties and microscopic electric charge fluctuations, offering fresh insights into the interaction of THz light with disordered materials.

Tsukuba, Japan—Electromagnetic waves in the gigahertz (GHz) range, such as those used in mobile communications, can readily pass through many types of glass. However, transmission significantly decreases at terahertz frequencies above a characteristic threshold. Although this phenomenon has been observed experimentally for some time, a quantitative model connecting it to the microscopic structure and dynamics of glass has been lacking.

To address this problem, the research team developed a continuum model that incorporates elastic heterogeneity in glass alongside microscopic charge fluctuations at atomic and molecular scales. This model describes how terahertz electromagnetic waves interact with vibrational dynamics in glass.

The researchers applied the model to glycerol glass, a representative molecular glass, and found that the calculations accurately reproduced the experimentally measured real and imaginary parts of the complex dielectric function across 0.3-2.5 THz. In addition, the model captured the transition from a resonance-like response below the boson-peak frequency to a broad relaxation-like response above it.

The analysis further showed that around the boson peak, the transverse contribution predominantly influences both the real and imaginary parts of the terahertz dielectric response, whereas the longitudinal contribution is comparatively small. This suggests that transverse shear dynamics play a pivotal role in the response. The model also replicated the nearly linear frequency dependence of the infrared light-vibration coupling coefficient observed near the boson peak.

These findings provide a framework for quantitatively linking terahertz absorption to charge fluctuations based on material-specific mechanical properties. The approach could facilitate the design and evaluation of glass materials with low permittivity and low dielectric loss, characteristics that are increasingly important for terahertz communications and photonic technologies.

###
This work was supported by JSPS KAKENHI Grant Nos. JP23H01139 and JP23K25836 (to T.M.), JP25H01519 and JP22K03543 (to H.M.), and JP24K08045 (to Y.F.); by the Asahi Glass Foundation (to T.M.); and by support from GIC & NGF (to T.M.).

Original Paper

Title of original paper:

Continuum model for the terahertz dielectric response of glasses

Journal:

Physical Review B

DOI:

10.1103/sjkh-zd6t

Correspondence

Assistant Professor MORI Tatsuya
Department of Materials Science, Institute of Pure and Applied Sciences, University of Tsukuba

Assistant Professor MIZUNO Hideyuki
Graduate School of Arts and Sciences, The University of Tokyo

Specially Appointed Associate Professor FUJII Yasuhiro
Institute for Open and Transdisciplinary Research Initiatives, The University of Osaka

Professor KOREEDA Akitoshi
Department of Physical Sciences, Ritsumeikan University

Related Link

Institute of Pure and Applied Sciences