Ultra-wide plasmonic tuning of semiconductor metasurface resonators on epsilon near zero media

Abstract: Fully reconfigurable metasurfaces would enable new classes of optical devices that provide unprecedented control of electromagnetic beamforms. The principal challenge for achieving reconfigurability is the need to generate large tunability of subwavelength, low-Q metasurface resonators. Here, we demonstrate large refractive index tuning can be efficiently facilitated at mid-infrared wavelengths using novel temperature-dependent control over free-carrier refraction. In doped InSb we demonstrate nearly two-fold increase in the electron effective mass leading to a positive refractive index shift ({\Delta}n>1.5) far greater than conventional thermo-optic effects. In undoped films we demonstrate more than 10-fold change in the thermal free-carrier concentration producing a near-unity negative refractive index shift. Exploiting both effects within a single resonator system, intrinsic InSb wires on a heavily doped (epsilon near zero) InSb substrate, we demonstrate dynamically tunable Mie resonances. The observed larger than line-width resonance shifts ({\Delta}{\lambda}>1.5{\mu}m) suggest new avenues for highly tunable and reconfigurable mid-infrared semiconductor metasurfaces.