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Magneto-transport controlled by Landau polariton states


Hybrid excitations, called polaritons, emerge in systems with strong light–matter coupling. Usually, they dominate the linear and nonlinear optical properties with applications in quantum optics. Here, we show the crucial role of the electronic component of polaritons in the magneto-transport of a cavity-embedded two-dimensional electron gas in the ultrastrong coupling regime. We show that the linear direct-current resistivity is substantially modified by the coupling to the cavity even without external irradiation. Our observations confirm recent predictions of vacuum-induced modification of the resistivity. Furthermore, photo-assisted transport in the presence of a weak irradiation field at sub-terahertz frequencies highlights the different roles of localized and delocalized states.

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Fig. 1: A quantum Hall system ultrastrongly coupled to a microwave cavity.
Fig. 2: Transport in vacuum fields.
Fig. 3: Transport with a small polariton population.
Fig. 4: Filling-factor-dependent photo-response reveals polariton branches and its decay channels.

Data availability

The datasets generated and analysed during the current study are available from the corresponding authors on reasonable request.


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We especially thank J. Andberger for performing many measurements confirming our results, P. Märki for valuable contributions to the measurement electronics and S. Rajabali for processing one of the transmission samples. The authors acknowledge financial support from ERC grant no. 340975 (MUSiC). The authors also acknowledge financial support from the Swiss National Science Foundation (SNF) through the National Centre of Competence in Research Quantum Science and Technology (NCCR QSIT).

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Authors and Affiliations



G.L.P.-B. developed the sample design and the fabrication. He also built the main magneto-transport set-up, developed the experimental technique, performed measurements and finite-element simulations. He wrote the paper. F.A. developed the experimental technique and the set-up, performed measurements and wrote the paper. E.R. performed the second set of measurements. F.V. developed an early experimental setup, performed early measurements and analysed early results. J.K. made THz-TDS measurements and scanning electron micrographs. M.B. grew the epitaxial 2DEG. N.B. and C.C. developed the theory on transport under illumination and wrote the paper. C.R. developed early sample designs and fabricated them. T.I. and K.E. provided critical know-how on transport and electronics to build the two transport set-ups. G.S. supported and designed experiments, set-ups and samples. He contributed to the data analysis and wrote the paper. J.F. designed the experiments, analysed the data, supervised the whole work and wrote the paper.

Corresponding authors

Correspondence to Gian L. Paravicini-Bagliani or Giacomo Scalari.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary Text, Supplementary Figs. 1–7 and Supplementary References.

Supplementary Video

Filling-factor-dependent photoresponse. Each colourmap frame corresponds to a measurement of the longitudinal photo response with the Landau level density of states aligning with the Fermi energy EF as shown on the left. The top and bottom panels of Fig. 4a represent two specific frames (in the beginning and middle of the video)

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Paravicini-Bagliani, G.L., Appugliese, F., Richter, E. et al. Magneto-transport controlled by Landau polariton states. Nature Phys 15, 186–190 (2019).

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