  We present a hybrid device platform for creating an electrically
reconfigurable metasurface formed by the integration of plasmonic
nanostructures with phase-change material germanium antimony telluride (GST).
By changing the phase of GST from amorphous to crystalline through Joule
heating, a large range of responses from the metasurface can be achieved.
Furthermore, by using the intermediate phases of GST, the metasurface can
interact with the incident light in both over-coupling and under-coupling
regimes, leading to an inherently broadband response. Through a detailed
investigation of the nature of the fundamental modes, we demonstrate that
changing the crystalline phase of the GST at the pixel-level enables an
effective control over the key properties (i.e., amplitude, phase, and
polarization) of incident light. This leads to the realization of a broadband
electrically tunable multi-functional metadevice enabling beam switching,
focusing, steering, and polarization conversion. Such a hybrid structure offers
a high-speed, broadband, and non-volatile reconfigurable paradigm for
electrically programmable optical devices such as switches, holograms, and
polarimeters.
