by University of Tsukuba
edited by Swati Mestri, reviewed by Andrew Zinin

Credit: Unsplash/CC0 Public Domain

Electromagnetic waves in the gigahertz (GHz) range, such as those used in mobile communications, can readily pass through many types of glass. However, transmission decreases significantly 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. The model describes how terahertz electromagnetic waves interact with vibrational dynamics in glass.

The paper is published in the journal Physical Review B.

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¨C2.5 THz. The model also 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.

Publication details
Tatsuya Mori et al, Continuum model for the terahertz dielectric response of glasses, Physical Review B (2026). DOI: 10.1103/sjkh-zd6t
Journal information: Physical Review B