STATUS OF PRECISION-MEASUREMENT OF THE QUANTUM HALL-EFFECT

When Klaus von Klitzing discovered the quantum Hall effect in 1980 he pointed out its great importance for metrology, both as a new experime nt for the determination of the fine structure constant and as a resis tance standard. It was a challenge to metrologists all over the world to work out methods for measuring this effect more and more precisely. The tremendous development of resistance measurement techniques in th e past 16 years is described. It has allowed a decrease in the uncerta inty by four orders of magnitude to be achieved and has been stimulate d by the discovery of the quantum Hall effect. The reproducibility of measurements of the quantized Hall effect has reached a level of uncer tainty of a few parts in 10(10). Experiments on the dependence of the quantized Hall resistance carried out using various samples of differe nt materials and with different properties are summarized. Experimenta lly determined values of the von Klitzing constant are compared with v alues which can be deduced from recent determinations of the fine stru cture constant. The most fascinating thing about the quantum Hall effe ct is that although no quantitative theory exists its high reproducibi lity has led to the world-wide agreement on this effect to be the basi s for the maintenance of the unit of resistance.