Landau polaritons in highly nonparabolic two-dimensional gases in the ultrastrong coupling regime
Janine Keller, Giacomo Scalari, Felice Appugliese, Shima Rajabali, Mattias Beck, Johannes Haase, Christian A. Lehner, W. Wegscheider, Michele Failla, M. Myronov, D. R. Leadley, James Lloyd‐Hughes, Pierre Nataf, Jérôme Faist
Abstract
We probe ultrastrong light-matter coupling between metallic terahertz metasurfaces and Landau-level transitions in high-mobility two-dimensional electron and hole gases. We utilize heavy-hole cyclotron resonances in strained Ge and electron cyclotron resonances in InSb quantum wells, both within highly nonparabolic bands, and compare our results to well-known parabolic AlGaAs/GaAs quantum well systems. Tuning the coupling strength of the system by two methods, lithographically and by optical pumping, we observe a behavior clearly deviating from the standard Hopfield model previously verified in cavity quantum electrodynamics: an opening of a lower polaritonic gap.