Investigation of the stability of graphene devices for quantum resistance metrology at direct and alternating current

Interlaboratory comparisons of the quantized Hall resistance (QHR) are essential to verify the international coherence of primary impedance standards. Here, we report on the investigation of the stability of p-doped graphene-based QHR devices at direct and alternating currents at CMI, KRISS, and PTB. To improve the stability of the electronic transport properties of the polymer-encapsulated devices, they were shipped in an over-pressurized transport chamber. The agreement of the quantized resistance with RK/2 at direct current was on the order of 1 nΩ Ω−1 between 3.5 and 7.5 T at a temperature of 4.2 K despite changes in the carrier density during the shipping of the devices. At alternating current, the quantized resistance was realized in a double-shielded graphene Hall device. Preliminary measurements with digital impedance bridges demonstrate the good reproducibility of the quantized resistance near the frequency of 1 kHz within 0.1 μΩ Ω−1 throughout the international delivery.