Avoiding common-mode artifacts when measuring 2D materials with high contact resistance
Measurements on two-dimensional materials pose a particular challenge due to their unique electronic properties. High contact resistance, in particular, can lead to unexpected artifacts in the measurement. Although measurements with a four-point arrangement minimize the influence of contact resistance, the voltmeter measures an "artifact voltage" (differential signal) in addition to the expected voltage. This error term is independent of the common-mode rejection ratio (CMRR) of the amplifier. Since this is an in-phase effect, this artifact is also difficult to detect. The causes are parasitic capacitances and leakage currents, which lead to the falsified voltage measurement. Important experimental and instrumental characteristics include the aforementioned contact resistance, the input resistance of the voltmeter, and the resistance of the voltmeter to ground.
A comparison between a setup with a classic lock-in amplifier and the setup with the modern M81-SSM system from Lake Shore Cryotronics shows drastic differences: While the conventional setup has an error of over 93%, the error with the M81-SSM is only 0.5%.
For this setup for measurement on a Hall bar sample, the M81-SSM system was selected with the BCS-10 current source module and the VM-10 voltmeter. With an input impedance of over 1 TΩ, the VM-10 is ideally suited for this measurement task. The M81-SSM enables precise measurement even with high contact resistances and is therefore a reliable solution for the electrical characterization of 2D materials.
Conclusion:
Taking common-mode artifacts into account is essential for the accuracy of transport measurements on 2D materials. Modern measurement systems such as the M81-SSM offer an effective way to suppress this error term thanks to their design.
This article summarizes the report "Common-mode Artifacts in 2D Materials with Significant Contact Resistance" prepared by our partner Lake Shore Cryotronics.
The complete report with calculations can be found on the Lake Shore website.
