We report the performance of a quantum Hall resistance standard based on epitaxial graphene maintained in a 5-T tabletop cryocooler system. This quantum resistance standard requires no liquid helium and can operate continuously, allowing year-round accessibility to quantized Hall resistance measurements. The ν = 2 plateau, with a value of RK/2, also seen as RH, is used to scale to 1 kΩ using a binary cryogenic current comparator (BCCC) bridge and a direct current comparator (DCC) bridge. The uncertainties achieved with the BCCC are such as those obtained in the state-of-the-art measurements using GaAs-based devices. BCCC scaling methods can achieve large resistance ratios of 100 or more, and while room temperature DCC bridges have smaller ratios and lower current sensitivity, they can still provide alternate resistance scaling paths without the need for cryogens and superconducting electronics. Estimates of the relative uncertainties of the possible scaling methods are provided in this report, along with a discussion of the advantages of several scaling paths. The tabletop system limits are addressed as are potential solutions for using graphene standards at higher currents.
An international comparison of dc resistance at 10 MΩ and 1 GΩ was organized under the auspices of the Consultative Committee for Electricity and Magnetism (CCEM) and piloted by the National Institute of Standards and Technology (NIST, USA). This CCEM comparison began in August 1996 and was completed in March 2000 with the participation of fourteen other national metrology institutes (NMIs). The travelling package included three wirewound 10 MΩ standards and three film-type 1 GΩ standards designed by the NIST. Results indicate that the differences at 10 MΩ and 1 GΩ between each laboratory's values and the respective reference value, are all within each laboratory's expanded relative uncertainty at a coverage factor k = 2.
We report the fabrication and measurement of top gated epitaxial graphene p-n junctions where exfoliated hexagonal boron nitride (h-BN) is used as the gate dielectric. The four-terminal longitudinal resistance across a single junction is well quantized at the von Klitzing constant with a relative uncertainty of 10−7. After the exploration of numerous parameter spaces, we summarize the conditions upon which these devices could function as potential resistance standards. Furthermore, we offer designs of programmable electrical resistance standards over six orders of magnitude by using external gating.
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