  We theoretically investigate the steady-state transmission of continuous
terahertz (THz) wave across a freestanding ferroelectric slab. Based on the
Landau-Ginzburg-Devonshire theory of ferroelectrics and the coupled equations
of motion for polarization and electromagnetic (EM) waves, we derive the
analytical expressions of the frequency- and thickness-dependent dielectric
susceptibility and transmission coefficient at the thin slab limit in the
harmonic excitation regime. When the slab thickness is much smaller than the
THz wavelength in the ferroelectric, the analytical predictions agree well with
the numerical simulations from a dynamical phase-field model that incorporates
the coupled dynamics of strain, polarization, and EM wave in multiphase
systems. At larger thicknesses, the transmission is mainly determined by the
frequency-dependent attenuation of THz waves in the ferroelectric and the
formation of a standing polarization/THz wave. Our results advance the
understanding of the interaction between THz wave and ferroelectrics and
suggest the potential of exploiting ferroelectrics to achieve
low-heat-dissipation, nonvolatile voltage modulation of THz transmission for
high-data-rate wireless communication.
