Terahertz signatures of quantum geometry in dual-gated moiré graphene

Collective excitations such as plasmons are predicted to encode the quantum geometry of moiré materials. Using on-chip terahertz spectroscopy, we measure gate-tunable plasmon resonances in bilayer graphene/hBN moiré superlattices, which arise due to finite-size, self-cavity effects. A coplanar stripline with a sub-100 nm gap above the sample allows for dual gating and the extraction of the complex cavity conductivity from 50 GHz to 1 THz. The spectra show widely tunable plasmon modes, revealing moiré-induced band hybridization and electron-hole asymmetry. Lorentzian fits indicate contributions to the Drude weight arising from the quantum metric. These results open a path toward a geometric understanding of the electrodynamics of moiré superlattices, to identify how topology and electronic correlations shape low-energy responses.