  Optical properties of planar thin film metamaterials were measured at room
and liquid nitrogen temperatures using terahertz time-domain spectroscopy. The
operation of metamaterials at cryogenic temperatures is anticipated to be a
promising path towards low-loss metamaterials since nonradiative losses are
strongly suppressed due to higher charge mobility. A 14% increase in the
quality factor of the resonances was experimentally observed. It was limited by
the high electron scattering rate due to defects in thin films. Supplementary
simulations assuming metamaterials made of thick films reveal a temperature
controlled behaviour and a 40% increase of the Q-factor at 10 K.
