Semiconductor split-ring resonators for thermally tunable, terahertz   metamaterials
  As the variation of temperature alters the intrinsic carrier density in a semiconductor, numerical simulations indicate that the consequent variation of the relative permittivity in the terahertz regime provides a way to realize thermally tunable split-ring resonators. Electromagnetic metasurfaces and metamaterials that are thermally tunable in the terahertz regime can thus be implemented. 
Jiaguang Han, Akhlesh Lakhtakia