Practice and theory


For more than 150 years we have used electrons for practical purposes. Yet they were only discovered in 1897. Early models described electrons in a metal as a gas. In 1956 the Russian physicist Lev Landau (Nobel Prize 1962) explained why electrons in a metal behave like nearly independent particles. Landau provided a model which can predict how electrons behave in increasingly sophisticated electronic applications. The whole microelectronics industry is based upon knowledge of how electrons move. First practice, then theory, then practice again in constant interplay. This is the stuff that science is made of.

Electrons in a magnetic field behave like a cloud of mosquitoes in a cross-wind. In an electrical conductor the magnetic wind pushes the electrons towards one edge. The potential rises in the direction of the wind – at right angles to the direction of the current. Edwin Hall discovered this phenomenon (the Hall effect) in 1879 when he was only 24 years old.

The Hall Effect

A magnetic field through a conductor creates a voltage (VH) at right angles to both the direction of current and the magnetic field.

The integer quantum Hall effect

Near absolute zero, in powerful magnetic fields and with the electrons forced to move in a plane, the Hall effect changes in steps.

The fractional quantum Hall effect

In Horst Störmer’s and Daniel Tsui’s experiments several new, unexpected notches and plateaux appeared in the quantised Hall effect.

Potential in leaps

In 1980 Klaus von Klitzing studied the Hall effect with new tools. He enclosed the electrons in an atom-thin layer. He cooled them to near absolute zero in very powerful magnetic fields. The Hall effect showed clear steps. Klaus von Klitzing received the Nobel Prize for his discovery in 1985. Yet his discovery did not disturb Landau’s foundation. The laws of quantum physics explained the steps and the electron’s charge was still undivided.

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