Precise comparisons of quantized Hall resistances

A method allowing the comparison of quantized Hall resistances R
H
with an uncertainty of ∼4 × 10
⁻⁹
is described. Results are presented for six heterostructures (five GaAs-Al
x
Ga
1−x
As type and one InGaAs-InP type). The differences between the quantized Hall resistances R
H
(2) or R
H
(4) for four different GaAs-based samples are lower than ±5 × 10
⁻⁹
.