Since the emergence of graphene, we have seen several proposals for the realization of Landau lasers tunable over the terahertz frequency range. The hope was that the non-equidistance of the Landau levels from Dirac fermions would suppress the harmful non-radiative Auger recombination. Unfortunately, even with this non-equidistance, an unfavourable non-radiative process persists in Landau-quantized graphene, and so far no cyclotron emission from Dirac fermions has been reported. One way to eliminate this last non-radiative process is to sufficiently modify the dispersion of the Landau levels by opening a small gap in the linear band structure. HgTe quantum wells close to the topological phase transition are a proven example of such gapped graphene-like materials. In this work we experimentally demonstrate Landau emission from Dirac fermions in such HgTe quantum wells, where the emission is tunable by both the magnetic field and the carrier concentration. Consequently, these results represent an advance in the realization of terahertz Landau lasers tunable by a magnetic field and gate voltage.
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Data are available from the corresponding author on reasonable request. The dataset will also be uploaded on the Recherche Data Gouv repository (https://recherche.data.gouv.fr) once the manuscript is accepted and published.
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This work was supported by the Terahertz Occitanie Platform (F.T., J.T.); by the CNRS through IRP ‘TeraMIR’ (F.T., M.O., V.I.G.); by the French Agence Nationale pour la Recherche for Colector (ANR-19-CE30-0032; F.T., M.O., V.I.G.), Stem2D (ANR-19-CE24-0015; J.T.) and Equipex+ Hybat (ANR-21 -ESRE-0026; F.T.) projects; by the European Union through the Flag-Era JTC 2019—DeMeGras project (ANR-19-GRF1-0006; F.T.) and the Marie-Curie grant agreement no. 765426 (S.G.), from the Horizon 2020 research and innovation program; and by the Center of Excellence (Center of Photonics), funded by The Ministry of Science and Higher Education of the Russian Federation (contract no. 075-15-2022-316; S.V.M., V.I.G.). We would like to acknowledge C. Lhenoret for technical support, L. Varani for financial support and W. Knap for fruitful discussions and valuable support. F.T. and C.C. would also like to thank S. Bonifacie for all of the passionate discussions, and for his friendship and his timeless presence.
The authors declare no competing interests.
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Gebert, S., Consejo, C., Krishtopenko, S.S. et al. Terahertz cyclotron emission from two-dimensional Dirac fermions. Nat. Photon. 17, 244–249 (2023). https://doi.org/10.1038/s41566-022-01129-1