Landauer resistivity dipole at one dimensional defect revealed via near-field photocurrent nanoscopy

TL;DR

This study uses near-field photocurrent nanoscopy to visualize Landauer resistivity dipoles at a graphene interface, revealing how local charge accumulation affects resistance at the nanoscale.

Contribution

It demonstrates a non-invasive method to experimentally observe Landauer resistivity dipoles at one-dimensional defects in graphene.

Findings

Landauer resistivity dipoles detected near charge neutrality point

Polarity of photocurrent matches applied voltage at low doping

Dipole signatures diminish at higher charge carrier densities

Abstract

The fundamental question how to describe Ohmic resistance at the nanoscale has been answered by Landauer in his seminal picture of the so-called Landauer resistivity dipole. This picture has been theoretically well understood, however experimentally there are only few studies due to the need for a non-invasive local probe. Here we use the nanometer lateral resolution of near-field photocurrent imaging to thoroughly characterize a buried monolayer - bilayer graphene interface as an ideal one dimensional defect for the Landauer resistivity dipole. Via systematic tuning of the overall charge carrier density and the current flow we are able to detect the formation of Landauer resistivity dipoles due to charge carrier accumulation around the one dimensional defects. We found that, for Fermi energy values near the charge neutrality point (i.e. at low hole or electron doping), the photocurrent exhibits the same polarity as the applied source-drain voltage, which is consistent with changes in carrier concentration induced by the Landauer resistivity dipoles. This signature is no longer evident at higher charge carrier density in agreement with the performed numerical calculations. Photocurrent nanoscopy can thus serve as non-invasive technique to study local dissipation at hidden interfaces.