The Quantum Hall Effect Gets More Practical

Abstract

Thin films of magnetic topological insulators can exhibit a nearly ideal quantum Hall effect without requiring an applied magnetic field. The quantum Hall effect is the striking quantization of resistance observed under a large applied magnetic field in two-dimensional electron systems like graphene. In a quantum Hall system, the transverse resistance (mea-sured across the width of the sample) takes on quantized values h/νe 2 , where h is Planck's constant, e the ele-mentary charge, and ν an integer or a fraction. The extreme precision with which the Hall resistance can be measured has important applications in metrology, pro-viding today's standard definition of the ohm. Another key feature of the effect is that the longitudinal resistance (measured along the length of the sample) vanishes: elec-trons can be transported without dissipation along the edges of the sample. Quantum Hall systems could thus act as perfect wires with little energy consumption.