Mechanical Activation of Terahertz Tunneling in Metallic Nanogaps

Abstract

Metallic nanogaps concentrate terahertz (THz) fields into deep subwavelength volumes and support field-driven electron tunneling when the insulating barrier becomes sufficiently narrow. Here, we demonstrate mechanical control of tunneling-mediated nonlinear THz transmission in a flexible nanogap metasurface. The metasurface consists of Au/PMMA/Au nanogaps fabricated on a polyethylene terephthalate substrate, enabling continuous tuning of the gap geometry through macroscopic bending. In the flat state, the resonant transmission exhibits only a weak dependence on the incident THz field strength. Upon bending, increasing the incident field strength induces pronounced resonance suppression accompanied by saturation of the voltage developed across the nanogaps. This nonlinear response is consistent with the opening of a field-dependent tunneling conduction channel through the mechanically narrowed PMMA barriers. Simmons-model calculations illustrate the strong increase in tunneling current density and the associated dissipative gap response as the local gap width approaches the few-nanometer regime. These results establish mechanical deformation as a macroscopic means of controlling tunneling-mediated THz nonlinearities in flexible metasurfaces.