Enigmatic materials that conduct electricity at only their surfaces, known as topological insulators, could be used to measure the fine structure constant, α — one of three factors that determine the speed of light.

Joseph Maciejko at Stanford University in California and his team propose measuring α by observing the quantized magnetoelectric effect (QME) — a predicted phenomenon in which an electric field induces magnetization in discrete quantum steps. The proposed experiment would use a layer of a topological insulator on top of a layer of ordinary insulator, all sitting in an external magnetic field. The authors say that measuring the polarization of light reflected off the surface of the topological insulator, and comparing this with the measurement of the polarization of light transmitted through the layers, will reveal a measurement of the QME — and hence α — in a way that is independent of the materials' properties.

Phys. Rev. Lett. 105, 166803 (2010)