Electrically programmable quantum resistance standards with epitaxial graphene PN junctions

Epitaxial graphene has been identified as an excellent platform for resistance standards based on the quantum Hall effect (QHE) because of the wide plateaus and large breakdown current. The bipolar nature of graphene also allows it to be electrically gated to form PN junctions for convenient scaling of QHE-based resistance standards. We have fabricated top gated epitaxial graphene PN junction samples using hexgonal boron nitride (hBN) as dielectric materials and have measured the samples with highly accurate resistance bridges. The four terminal longitudinal resistance across a single junction is well quantized at h/e² with an error of about 0.1 ppm on one edge and is around milli-ohm on the opposite edge. We have determined the optimal conditions where the breakdown current is maximized. Measurement using cryogenic current comparator is ongoing and array of PN junctions is under fabrication. Our work opens the possibility to realize high accuracy electrical resistance standards that are programmable using external gating.