Theoretical research on an optically and thermally tunable terahertz absorber based on epsilon-near-zero mode

In this paper, we propose a tunable terahertz (THz) absorber with optical and thermal modulation capabilities. The absorber employs photoconductive silicon in the top resonant structure to excite plasmon modes, while an indium antimonide (InSb) thin film inserted between the resonator and dielectric layer enables epsilon-near-zero mode excitation. The mutual coupling of these two modes achieves high-efficiency absorption. Separate control of optical illumination and environmental temperature allows flexible manipulation of the absorption. Simulation results demonstrate that at room temperature, the device exhibits >90% absorption spanning from 1.52 to 1.80 THz. When the temperature decreases to 240 K, the >90% absorption band redshifts to 0.93–1.71 THz. Optical modulation enables the suppression of absorption within this range, reducing it from over 90% to below 15%. Comprehensive theoretical frameworks, including equivalent circuit modeling and multiple interference theory, were employed to elucidate the working mechanism and assess the reliability. This work demonstrates significant potential for applications in thermal management, plasmonic devices, and fundamental physics research.