Terahertz Electrodynamics of $180^\circ$ Domain Walls in Thin   Ferroelectric Films
  We investigate oscillation dynamics of a periodic structure of the $180^\circ$ domain walls in nanometricaly thin substrate-deposited ferroelectric films and superlattices. We calculate dynamic permittivity of such structures and reveal a collective resonance mode, which in the typical ferroelectric compounds, PbTiO3/SrTiO3, lies in the sub- and low THz frequency range of 0.3-3THz. We propose the reflection-absorbtion spectroscopy experiments to observe this mode. 
Igor Luk'yanchuk, Alexey Pakhomov, Ana\"is Sen\'e, Alexandr Sidorkin   and Valerii Vinokur
cond-mat.mtrl-sci