Quantitative measurement of giant and quantized microwave Faraday rotation

We report quantitative microwave Faraday rotation measurements conducted with a high-mobility two-dimensional electron gas (2DEG) in a GaAs/AlGaAs semiconductor heterostructure. In a magnetic field, the Hall effect and the Faraday effect arise from the action of Lorentz force on electrons in the 2DEG. As with the Hall effect, a classical Faraday effect is observed at low magnetic field along with a quantized Faraday effect at high magnetic field. The high electron mobility of the 2DEG enables a giant single-pass Faraday rotation of θFmax≃45(≃0.8 rad) to be achieved at a modest magnetic field of B≃100 mT. In the quantum regime, we find that the Faraday rotation θF is quantized in units of α∗=2.80(4)α, where α≃1/137 is the fine-structure constant. The enhancement in rotation quantum α∗>α is attributed to electromagnetic confinement within a waveguide structure.