Landauer Resistivity Dipole at One-Dimensional Defect Revealed via near-Field Photocurrent Nanoscopy

The fundamental question of how to describe ohmic resistance at the nanoscale was answered by Landauer in his seminal picture of the Landauer resistivity dipole (LRD). While this picture is theoretically well understood, experimental studies remain scarce due to the need for noninvasive local probes. Here, we use the nanometer lateral resolution of near-field photocurrent imaging to thoroughly characterize a monolayer-bilayer graphene interface. Via systematic tuning of charge carrier density and current flow, we detected charge carrier accumulation around this nearly ideal one-dimensional defect due to the formation of the LRDs. We found that, at low doping levels, the photocurrent exhibits the same polarity as the applied source-drain voltage, reflecting carrier concentration changes induced by the LRDs. This signature disappears at higher charge carrier densities in agreement with the numerical calculations performed. Photocurrent nanoscopy can thus serve as a noninvasive technique to study local dissipation at hidden interfaces.