Researchers are working to redefine two SI units — those for mass (the kilogram) and current (the ampere). The aim is for the definitions to be based on relationships between fundamental constants, so researchers are testing whether phenomena that relate the constants are always the same.
Jan-Theodoor Janssen of the National Physical Laboratory in Teddington, UK, and his colleagues have shown that one such relationship, the quantum Hall effect — which relates the electron charge and Planck's constant to resistance — holds in completely different materials. The researchers measured the resistance associated with the quantum Hall effect in both graphene and gallium arsenide, and found that it was the same, to an uncertainty of just 86 parts per trillion — a sign that the effect is a sound foundation for SI-unit redefinition.
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Redefining the kilogram. Nature 477, 512 (2011). https://doi.org/10.1038/477512c
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DOI: https://doi.org/10.1038/477512c
