Thermal tunability in terahertz metamaterials fabricated on strontium   titanate single crystal substrates
  We report an experimental demonstration of thermal tuning of resonance frequency in a planar terahertz metamaterial consisting of a gold split-ring resonator array fabricated on a bulk single crystal strontium titanate (SrTiO3) substrate. Cooling the metamaterial starting from 409 K down to 150 K causes about 50% shift in resonance frequency as compare to its room temperature resonance, and there is very little variation in resonance strength. The resonance shift is due to the temperature-dependent refractive index (or the dielectric constant) of the strontium titanate. The experiment opens up avenues for designing tunable terahertz devices by exploiting the temperature sensitive characteristic of high dielectric constant substrates and complex metal oxide materials. 
Ranjan Singh, Abul K. Azad, Q. X. Jia, Antoinette J. Taylor, and   Hou-Tong Chen
physics.optics cond-mat.mtrl-sci