Comparative measurements of quantum resistance standards made of graphene and GaAs/AlGaAs.

For the future representation and dissemination of the unit ohm of resistance, graphene-based and GaAs-based quantum Hall (QH) resistors from PTB's own production were compared against each other at the highest level of precision. The comparison was performed indirectly using a conventional reference resistor and shows that the universality of the quantum Hall resistance in the material systems GaAs/AlGaAs and graphene is given at an accuracy level of two nΩ per Ω.

In the course of the investigations, the graphene-based and GaAs-based QH samples were first comprehensively pre-characterized in a cryomagnetic system according to the guidelines for the application of the QH effect in resistance metrology [Delahaye, Jeckelmann, Metrologia 40, 217 (2003)]. In each case, following these preliminary tests, the reference resistor was calibrated with the QH resistances using a high-precision resistance measuring bridge (based on a cryogenic current comparator). Quantitatively considering the series resistance of the QH resistors as well as the time drift, pressure and temperature dependencies of the reference resistor, the respective measured values were found to agree within the expanded measurement uncertainty of 2×10^-9, demonstrating the consistency of the QH resistance values in the devices fabricated from graphene and GaAs.

In further investigations, the current-carrying capacity of graphene-based QH resistors manufactured by PTB was also investigated. Here, it was shown that the resistance quantization is given at a magnetic field of B = 6 T and at a temperature of T = 4.2 K up to currents of 230 µA (for comparison: resistor calibrations as mentioned above are typically performed at currents of about 40 µA). These high breakdown currents of the graphene quantum resistors can be beneficial for further applications in metrology.

Overall, the advantages of graphene-based quantum resistors compared to conventional GaAs quantum resistors enable the technically simplified quantum-based representation of the unit ohm. The usability at relatively low magnetic fields and relatively high temperatures (which can be provided by means of modern cryo-cooler magnet systems) open up new application perspectives also in the field of industry and calibration laboratories.

Figure: Calibration values of a 100-Ω reference resistor obtained by comparisons with graphene- and GaAs-based quantum resistors (blue and red dots, respectively). The discernible differences in the measurement data from the two measurement campaigns reflect the drift of the (conventional) reference resistor over time. The inset shows a photo of a graphene quantum resistor in the sample holder.

Contact persons: 

Mattias Kruskopf and Atasi Chatterjee

Department 2.6 „Electrical Quantum Metrology"

mattias.kruskopf@ptb.de

atasi.chatterjee@ptb.de