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.

Abstract-Strong-Coupled Collective Cyclotron Resonance and Terahertz Cavity Photon in 2D Electron Gases

September 16, 2015 4:00PM to 5:00PM

PRESENTER 

Qi Zhang, Rice University

 

        LOCATION 

Building 440, Room A105

   

            

                        

http://www.anl.gov/events/strong-coupled-collective-cyclotron-resonance-and-terahertz-cavity-photon-2d-electron-gases

Achieving strong light-matter interaction in low-dimensional solid state systems is essential for both fundamental studies and device applications of cavity quantum electrodynamics (QED). It is particularly interesting to understand and even control the dynamics of collective excitations in solid states, when they are strongly coupled to cavity photons. A Landau-quantized, high-mobility two-dimensional electron gas (2DEG) provides a uniquely clean and tunable semiconductor system in which to explore strong light-matter interaction with many-electron states. In this talk, I will first show how rapidly a superposition of massively degenerate Landau levels loses its coherence in the free space.

We observed a collective radiative decay, or superradiance, of cyclotron resonance (CR) in 2DEG with time-domain terahertz magneto-spectroscopy. In the second part, I will demonstrate the strong-coupling between the cyclotron resonance and THz cavity photons. We observed Rabi oscillation in time domain, as well as the collective vacuum Rabi splitting. We significantly suppressed the superradiance decay of CR by the high-Q THz cavity, and resolved an ultra-narrow intrinsic CR linewidth (5 GHz). Our method may also apply to various correlated 2D systems with collective THz excitations. It opens an access to the intriguing physics of THz many-body cavity-QED.