Universal Singular Behavior is Observed in Quantum Hall Effect

Almost eight years after the discovery of the quantum Hall effect, a group led by Daniel Tsui (Princeton University) has observed universal scaling behavior that might provide an important clue to how the effect could be reconciled with the quantum theory of electrical resistance. At issue is a scaling law of that theory. As enunciated in 1979, the law applies only to electrons in the absence of a magnetic field. If, however, the law also applied to electrons in the presence of the strong magnetic fields used in quantum Hall effect measurements, then both the Hall conductance and the longitudinal conductance of electrons confined in a plane would have a vanishingly small value. (In Hall effect measurements, the sample is placed in perpendicular electric and magnetic fields. The Hall conductance is a measure of the current flow in a direction normal to both the electric field and the magnetic field.)