Giant terahertz near-field enhancement by two-dimensional plasmons
  We consider a periodically gated two-dimensional electron system, with a central gate finger biased independently creating a tunable plasmonic cavity in a planar plasmonic crystal. We demonstrate that the plasmons resonantly excited in the periodic plasmonic lattice by incident terahertz radiation can strongly pump the cavity plasmon modes leading to a deep sub-wavelength concentration of terahertz energy with giant electric field enhancement factor up to 10000. 
Arthur R. Davoyan, Vyacheslav V. Popov and Sergey A. Nikitov
physics.optics