Ultrafast Terahertz Nanoplasmonic Platform for Subpicosecond Charge–Voltage Characterization in Metal–Insulator–Metal Nanogaps

We construct a platform for probing capacitive phenomena with subpicosecond (subps) temporal resolution, utilizing terahertz (THz) nanoplasmonics. The system employs metal nanoslits that function as parallel nanocapacitor structures, integrated with THz time-domain spectroscopy. By analyzing both incident and transmitted THz pulses, we directly correlate the ultrafast current induced within the nanogap structure with the resulting charge accumulation and voltage drop, revealing an effective capacitive response. This enables the direct extraction of charge–voltage ( Q–V ) characteristics of nanometer-thick dielectric layers, demonstrated here using aluminum oxide (Al 2 O 3 ). Our approach establishes a versatile methodology for subps time-resolved characterization of dielectric responses in nanostructures, opening pathways for studying ultrafast electronic dynamics and emergent phenomena in quantum materials.