Dynamic dual-mode terahertz device with nonvolatile switching for integrated on-chip and free-space applications.

Terahertz communication systems demand versatile devices capable of simultaneously controlling propagating waves and surface plasmon polaritons (SPPs) in far-field (FF) and near-field (NF) channels, yet existing solutions are constrained by volatile operation, single-function limitations, and the inability to integrate NF and FF functionalities. Here, we present a nonvolatile reconfigurable terahertz metasurface platform leveraging the phase-change material GeSbTe(GST) to achieve on-demand dual-channel modulation-a first in the terahertz regime. By exploiting the stark conductivity contrast of GST between amorphous and crystalline states, our design enables energy-efficient switching between NF-SPP manipulation and FF-wavefront engineering without requiring continuous power input. Experimental validation demonstrates two devices: Device I dynamically transitions between NF SPP focusing and FF vortex beam generation, while Device II toggles NF anomalous SPP focusing and FF holographic imaging. The metasurface uniquely integrates simultaneous amplitude/phase control for SPPs and free-space waves, overcoming the single-channel limitations of prior works. With reversible switching cycles and nonvolatile state retention (>10 years), this platform bridges the gap between on-chip plasmonics and free-space terahertz technologies, offering transformative potential for applications in 6 G communication, encrypted data storage, and multifunctional metasensors.