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New experiments on the two-dimensional electrons in GaAs-Al0.3{Ga}0.7$As heterostructures at $T{~}0.14$ K and $B<~190$ kG demonstrate that the quantum number of the quantized Hall resistance, close to $1/3$ filling of the last Landau level, is $1/3$ to better than 1 part in ${10}⁴$.
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Tsui et al. (1983) studied this question.
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