Nano-imaging of quantum geometric photocurrents in crystalline multilayer graphene

The interplay between light and the geometric structure of electron wavefunctions can generate unconventional photocurrents in the absence of external electrical, magnetic, or thermal drives. Unlike photothermoelectric currents, quantum geometric photocurrents are intrinsic bulk responses that do not require junctions, edges, or variations in Seebeck coefficients. Two primary forms of such bulk photovoltaic currents are the shift and injection currents, arising respectively from real-space displacements of electron density and momentum-space asymmetries in carrier populations.

Here, we report nanoscale imaging of gate-tunable quantum geometric photocurrents in crystalline multilayer graphene using near-field infrared photocurrent nanoscopy. Beyond the rich allotrope-dependent behavior of shift and injection currents, we observe local hysteresis of shift currents within ferroelectric domains of noncentrosymmetric graphene. Furthermore, employing a confocal plasmonic resonator with a spherical tip, we reveal the nanoscale texture of polariton-drag–enhanced quantum geometric photocurrents in Bernal bilayer graphene close to neutrality. Our nano-infrared photocurrent experiments not only facilitate the understanding of nonlinear optical conductivities of quantum matter, but also open the pathway for ferroelectric and optoelectronic devices based on quantum geometry.