Quantized Hall resistance measurement at the NML

An automatic measurement system has been used to determine the values of quantized Hall resistances RH in terms of the National Measurement Laboratory (NML) realization of the International System (SI) ohm. The quantized Hall resistances of two GaAs-AlGaAs heterostructures were measured. The n = 2 step of one heterostructure and the n = 4 step of the other were measured over a seven-month period. A weighted mean of these determinations gave a value for the quantity RH(n = 1) of 0.383 ppm (0.078 ppm one-standard-deviation (1σ) uncertainty) above the nominal 25 812.80 Ω in SI units.