Abstract-Terahertz dynamics of a topologically protected state: Quantum Hall effect plateaus near the cyclotron resonance of a two-dimensional electron gas

A. V. Stier, C. T. Ellis, J. Kwon, H. Xing, H. Zhang, D. Eason, G. Strasser, T. Morimoto, H. Aoki, H. Zeng, B. D. McCombe, and J. Cerne

https://journals.aps.org/prl/accepted/7407eY6bA1211624e5cb9524f017aaf11454ad9dc

We measure the Hall conductivity of a two-dimensional electron gas formed at a GaAs/AlGaAs heterojunction in the terahertz regime close to the cyclotron resonance frequency using highly sensitive Faraday rotation measurements. The sample is electrically gated, allowing the electron density to be changed continuously by more than a factor of three. We observe clear plateau- and step-like features in the Faraday rotation angle vs. electron density and magnetic field (Landau-level filling factor) even at fields/frequencies very close to cyclotron resonance absorption. These features are the high frequency manifestation of quantum Hall plateaus - a signature of topologically protected edge states. We observe both odd and even filling factor plateaus and explore the temperature dependence of these plateaus. Although dynamical scaling theory begins to break down in the frequency region of our measurements, we find good agreement with theory.