ACS Photon. 1, 833–839 (2014)

Optically-controlled reversible switching of the resonances of optical nanoantennas is possible by covering them with a thin layer of a phase-change material, say researchers in Germany and the USA. The team, from RWTH Aachen University, SLAC National Accelerator Laboratory and Stanford University, report how femtosecond pulses from a Ti:Sapphire laser can be used to trigger amorphous-to-crystalline phase transitions in a thin film of Ge3Sb2Te6 (GST) by heating it. Changing the structural phase of GST shifts the spectral resonance of an aluminium nanoantenna, located underneath, as the permittivity of the GST changes. In particular, the refractive index of GST changes from a value of 3.56 in the amorphous phase to 6.33 in the crystalline phase. Experiments with aluminium antennas that were 400 or 500 nm in length underneath a 50-nm-thick layer of GST show a clear change in the infrared reflection spectra. The approach means that antennas within an array can be individually addressed and independently controlled by optical excitation. It is postulated that the scheme could be useful for creating plasmonic and metamaterial devices that are reconfigurable.