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 theta(max)(F) similar or equal to 45 degrees (similar or equal to 0.8 rad) to be achieved at a modest magnetic field of B similar or equal to 100 mT. In the quantum regime, we find that the Faraday rotation theta(F) is quantized in units of alpha* = 2.80(4)alpha, where alpha similar or equal to 1/137 is the fine-structure constant. The enhancement in rotation quantum alpha* > alpha is attributed to electromagnetic confinement within a waveguide structure.