We present a combined experimental and theoretical study of photovoltage generation in a bilayer graphene (BLG) transistor structure exposed to subterahertz radiation. The device possesses a global bottom and split top gate, enabling the formation of a tunable p–n junction with controllable band gap and carrier densities at both sides. Measurements show that the photovoltage arises primarily through a thermoelectric mechanism driven by heating of the p–n junction in the middle of the channel. We provide a theoretical justification for the excitation of two-dimensional plasmons at a record-low frequency of 0.13 THz, which manifests itself as characteristic oscillations in the measured photovoltage. These plasmonic oscillations, activated by a decrease in charge carrier concentration due to opening of the band gap, lead to a local enhancement of the electromagnetic field and an increase in the carrier temperature in the junction region. The record-low frequency of plasmon resonance is enabled by the low carrier density achievable in the bilayer graphene upon electrical induction of the band gap.
Moiseenko et al. (2025) studied this question.