Tunable nonlinear optical resonances in Landau-quantized graphene

Tunable nonlinear optical resonances in Landau-quantized graphene

König-Otto, J. C.; Wang, Y.; Belyanin, A.; Berger, C.; de Heer, W. A.; Orlita, M.; Venanzi, T.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.

Graphene has been in discussion as a candidate as a strong THz nonlinear material for a long time, because of its linear band structure [1,2]. However, an experimental demonstration of strong nonlinearities in Graphene in this spectral range is still missing. For Landau-quantized Graphene, in which the absorption is resonantly enhanced for allowed transitions between the Landau-levels, theory predicts a strongly enhanced nonlinearity, too [3]. In our joint experimental and theoretical work we study the third order nonlinearity in Landau-quantized graphene by employing a degenerate timeintegrated four-wave mixing experiment (FWM) in the mid-infrared spectral range. The free-electron laser FELBE was tuned to a photon energy of 78meV and the graphene sample was kept at 10K in a thin helium gas atmosphere. The magnetic field was set to 4.5T bringing the LL-1→LL0 and LL0→LL1 transition into resonance with the linearly polarized beams (see Fig.1a). The measured FWM signal (see Fig.1c) features a faster dynamics than the pump-probe signal (see Fig.1b) and is beyond the time resolution of our experiment. Nevertheless, we can recover the expected field dependencies of the studied third order nonlinearity in the experiment. The resonance behavior is measured by sweeping the magnetic field and is in agreement with our theoretical calculation. Furthermore, we derive a value of χ(3) from our experimental data that confirms the predicted strongly enhanced nonlinearity [4].
[1] S. A. Mikhailov and K. Ziegler, J. Phys.: Condens. Matter, 20, 384204, (2008)
[2] Z. Zhang and P. L. Voss, Opt. Lett., 36, 4569, (2011)
[3] X. Yao and A. Belyanin, Phys. Rev. Lett., 108, 255503, (2012)
[4] J. C. König-Otto, Y. Wang, A. Belyanin, C. Berger, W. A. de Heer, M. Orlita, A. Pashkin, H.
Schneider, M. Helm, and S. Winnerl, Nano Lett., 17, 2184, (2017)

Keywords: graphene; Landau-quantized graphene; nonlinear optics; carrier dynamics; spectroscopy

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Publ.-Id: 25942