Thought for the month

“The way to get things done is not to mind who gets the credit for doing them.” Benjamin Jowett, teacher and theologian (1817 – 93).

Thursday, 3 November 2011

A kilogram of graphene?

Research at the National Physical Laboratory (NPL) using graphene is underpinning a big change to the SI system of units. The goal being to relate all of the unit definitions to fundamental constants of nature. One of the key units to be redefined is the kilogram, currently defined by a physical lump of platinum-iridium. The other is the ampere. The goal is to define the kilogram in terms the Planck constant, h, and the ampere in terms of the electron charge, e. The Quantum Hall effect defines a relationship between h and e and is therefore key in any 'quantum-based' redefinition of mass and current. Experiments tested the quantum Hall effect in different materials in order to prove whether or not it is truly universal. NPL compared the quantum Hall effect in graphene with that observed in GaAs/AlGaAs and confirmed that the quantum Hall effect is truly universal with an uncertainty level of several parts in 1011, thus supporting the quantum based redefinition of both the kilogram and ampere.

The full paper is available this link.

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