Cryogenic Photovoltage Nanoscopy in 2D Moiré Lattices.

Since the discovery of magic-angle graphene, the landscape of 2D moiré materials has expanded significantly, exhibiting unique quantum states such as superconductivity, fractional Chern insulators, and topological orders. Unraveling the microscopic ground states of these systems requires advanced experimental techniques to probe the parameter space underlying various broken-symmetry phases. Here, we present a novel method for investigating the local thermoelectric properties of strongly correlated materials. Using a cryogenic near-field optical microscope, we generate nanometer-scale hotspots over planar 2D devices. Through the Shockley-Ramo theorem and intrinsic sample inhomogeneities, locally induced photocurrents propagate toward globally positioned contacts, where they are detected via a lock-in amplifier. We will outline the methodology and demonstrate how it enables us to discern scattering rate asymmetries around correlated gaps in twisted symmetric trilayer graphene, a member of the magic-angle graphene family.