Quantum Hall Science: A Platform for New Science and Applications
The date 20.5.2019 was a historic day for the Quantum Hall Effect (QHE) and our international measurement system of units. Since that day, constants of nature form the basis of our International System of Units (SI units). As a consequence of this change, the ampere is determined by the fixed value of the electron charge e and the kilogram by a fixed value for the Planck constant h. This also determines the value of the quantized Hall resistance h / e². Interestingly, it is now also possible to realize an electronic kilogram with the help of electrical quantum phenomena (Josephson Effect and quantum Hall effect). Quantum Hall arrays allow the realization of resistance standards from 100 Ohm to 10 000 000 Ohm.
Even if the quantum Hall effect shows a universal behavior, a microscopic picture of the current flow in real quantum Hall devices is complicated and does not agree with edge current pictures in textbooks. Experimental facts will be presented.
In addition, quantum Hall systems are an ideal platform for basic research on interacting two-dimensional electron systems. Recent experimental results obtained with high quality 2-dimensional electron systems in graphene or GaAs and ZnO heterostructures will be summarized.