The Hall effect, a fundamental technique for material characterization, is formed when a magnetic field deflects the flow of electrons sideways and leads to a voltage drop across the transverse direction. In 1980, a surprising observation was made when measuring the Hall effect for a two-dimensional (2D) electron gas trapped in a semiconductor structure -- the measured Hall resistivity showed a series of completely flat plateau, quantized to values with a remarkable accuracy of one part in 10 billion. This became known as the QHE.
QHE has since revolutionized our fundamental understanding of condensed matter physics, generating a vast field of physics research. Many new emerging topics, such as topological materials, can also be traced back to it.
Discovery - Researchers - Possibility - QHE - Systems
Soon after its discovery, researchers pursued the possibility of generalizing QHE from 2D systems to three dimensions (3D). Bertrand Halperin predicted that such a generalized effect, called the 3D QHE, is indeed possible in a seminal paper published in 1987. From theoretical analysis, he gave signatures for 3D QHE and pointed out that enhanced interactions between the electrons under a magnetic field can be the key to drive a metal material into the 3D QHE state.
30 years have passed since Halperin's prediction and while there have been continuing efforts in trying to realize 3D QHE in experiment, clear evidence has been elusive due to the stringent conditions required for 3D QHE -- the material needs to be very pure, have high mobility, and low carrier density.
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