Quantized Hall resistance measurement at the NML

An automatic measurement system has been used to determine the values of quantized Hall resistances R
H
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 R
H
(n = 1) of 0.383 ppm (0.078 ppm one-standard-deviation (1σ) uncertainty) above the nominal 25 812.80 Ω in SI units.