Broadband terahertz absorber with tunable frequency and bandwidth by using Dirac semimetal and strontium titanate.

A bifunctional broadband absorber in the terahertz band based on patterned bulk Dirac semimetal (BDS) and strontium titanate (STO) is proposed. The properties of the absorber are investigated using the finite-difference time-domain (FDTD) method. The results show that the width of absorption can be modulated from 0.59 THz to 0.7 THz when the Fermi energy of the BDS is independently shifted from 40 meV to 50 meV. By tuning the temperature from 250 K to 400K, the center frequency of the broadband absorption spectrum can be changed from 1.311 THz to 1.505 THz, and the absorption bandwidth broadens from 0.66 THz to 0.81 THz. In addition, the simulation results show that the absorber is insensitive to electromagnetic wave polarization, and can still maintain a stable broadband absorption effect when the oblique incidence is within 40° for TE and TM modes. Based on the impedance matching theory, the physical mechanism of the broadband absorption is analyzed theoretically. This work can provide an alternative way to design high-performance multifunctional tunable terahertz devices.