Quantized Microwave Faraday Rotation

The phenomenon of rotation of polarization in the presence of static magnetic field known as Faraday rotation [1] is very well known. Here we present the quantitative observation of microwave Faraday rotation conducted with GaAs/AlGaAs semiconductor heterostructure. The microwave Faraday rotation observed in high mobility two-dimensional electron gas arises as a result of cyclotron motion of charge carriers. The Faraday rotation induced can be understood by Fresnel analysis for the transmission of right and left handed circularly polarized microwaves. As with the Hall effect, a continuous classical as well as quantized Faraday rotation is observed. In the quantum Hall regime, the Faraday rotation is quantized in units of fine structure constant. The dielectric response of the semiconductor host, and the modification of the wave impedance and field distribution by a wave guide [2] will lead to a modification of the quantized Faraday rotation away from the vacuum fine structure constant, α ≈ 1/137. The effect of frequency dependent electromagnetic confinement can be accounted with an effective fine structure constant α*.

[1] M. Faraday, Phil. Trans. Roy. Soc. London 136, 1 (1846).
[2] D. L. Sounas and C. Caloz, IEEE Trans. Microwave Theory Tech. 60, 901 (2012).