Magnetotransport on the nano scale

Abstract

Transport experiments in strong magnetic fields show a variety of fascinating phenomena like the quantum Hall effect, weak localization or the giant magnetoresistance. Often they originate from the atomic-scale structure inaccessible to macroscopic magnetotransport experiments. To connect spatial information with transport properties, various advanced scanning probe methods have been developed. Capable of ultimate spatial resolution, scanning tunnelling potentiometry has been used to determine the resistance of atomic-scale defects such as steps and interfaces. Here we combine this technique with magnetic fields and thus transfer magnetotransport experiments to the atomic scale. Monitoring the local voltage drop in epitaxial graphene, we show how the magnetic field controls the electric field components. We find that scattering processes at localized defects are independent of the strong magnetic field while monolayer and bilayer graphene sheets show a locally varying conductivity and charge carrier concentration differing from the macroscopic average.

Electronic Transport Properties of 1D‐Defects in Graphene and Other 2D‐Systems

“…As can be seen, the spread of the values is quite large. As mentioned above, this is at least partially due to inhomogeneities and local disorder in the system as well as the individual structural and electronic properties of each defect . We propose a similar scattering mechanism as for the SiC‐substrate step.…”

“…obtained the only results up to now with . By analyzing a large number of STP‐datasets studies, Druga and Willke et al . could show that both the defect resistance for the line defects discussed above and for graphene sheet areas show a large standard deviation of the individual local sheet resistance values.…”

“…The resistance was found to increase roughly linearly with the number of substrate steps involved. Different values for the defect resistance at substrate steps and ML/BL‐interfaces have been reported in the following . In Table we collect the values for the resistance of all types of extended defects in graphene on SiC that have been analyzed locally up to now.…”

“…A local change in doping, wavefunction mismatch, and tunneling across potential barriers and between layers have been proposed to cause the dominating scattering for SiC‐substrate steps and monolayer(ML)‐bilayer(BL) interfaces, respectively as sketched in figure d. In the following, we discuss the scattering mechanisms at all defects in greater detail.…”

“…While several experimental techniques have been used to explore the role of defects on transport, scanning probe methods (SPM) are indubitably advantageous to access the defect structures along with the voltage drop and the electron flow on a microscopic scale. In particular, the scanning tunneling microscopy (STM)‐based techniques of scanning tunneling potentiometry (STP) and 4‐point‐probe (4PP) microscopy have been used to study the electron transport processes from mesoscopic dimensions down to the atomic scale. In addition, Kelvin probe force microscopy (KPFM), conductive atomic force microscopy (AFM), low energy electron potentiometry as well as conventional transport experiments have been used to study local transport and scattering at defects.…”