Characterization of Closed-Cycle Toploader for Quantum Resistance Standard in Graphene at KRISS

We report on the preliminary characterization of a toploading closed-cycle cryomagnet for the quantized Hall resistance (QHR) standard at KRISS. A toploading probe, built with coaxial cables, is designed to realize QHR in graphene at direct and alternating current by utilizing a pulse-tube cryomagnet with a base temperature of 3 K and a maximum magnetic field of 7 T. To reduce vibrations, a mass reservoir and an acoustic enclosure are introduced for a remote rotary valve and a connecting flexible hose. The vibration-induced current in the coaxial cable of the probe is investigated as a function of frequency. We also investigate the degree of equivalence between graphene-based QHR in the dry toploader and GaAs-based QHR in a conventional wet cryomagnet with a 1 kΩ resistance reference and a cryogenic current comparator.