Orateur
Description
Quantum electrical standards in the International System of units (SI) are challenging to put in practice together as their working conditions are nowadays intrinsically incompatible. The magnetic field required to realize the quantum Hall effect for the primary resistance standard prevents superconductivity, which is at the core of the quantum voltage standard through the AC Josephson effect. Considerable efforts are being made to simplify access to SI units through the development of a quantum multimeter. Here we explore the potential of devices made from graphene encapsulated in hexagonal boron nitride (h-BN) as a promising platform to host the two quantum effects. High mobilily quantum Hall devices have been shown to allow the Hall resistance quantization at low magnetic field (~ 1 T). We first characterise the graphene junction in its DC regime, and then observe particularly resilient phase-locked Shapiro plateaus under RF illumination at temperatures from 7 mK up to above 1.5 K [1]. Half-integer Shapiro steps also manifest at fRF = 8.8 GHz, which may indicate a nonsinusoidal current-phase relation (CPR) and thus a highly transparent junction [2]. We present our efforts into identifying limiting factors of the accuracy of the n = 1 Shapiro plateau as a function of experimental parameters (such as RF power, temperature, DC current bias, time and measurement setup).