Frederic Teppe
L2C, UMR CNRS 5221, Montpellier University, 34095 Montpellier, France.

“Probing Dirac and Kane fermions in HgCdTe crystals by Terahertz/MIR magneto-spectroscopy “

Topological phase transitions in solids are characterized by a band gap closing inducing a linear band dispersion associated with the creation of semi-relativistic massless quasi-particles. It turns out that HgCdTe-based heterostructures can be engineered to fabricate “gapped-at-will” structures. Therefore, 1D [1], 2D [2] and even 3D [3] massless particles can be observed in topological phase transitions driven by intrinsic (quantum well thickness, Cd content) and external (magnetic field, temperature or pressure) physical parameters. So far, the phases of 2D [1] and 3D [4] topological insulator have already been experimentally demonstrated in HgCdTe-based heterostructures. More recently, clear experimental evidence of the existence of 3D electronic states with conical-like spectrum was obtained in HgCdTe bulk films at specific Cd content [3]. These 3D massless particles, called Kane fermions, have unique symmetry properties, which are not equivalent to any well-known case of massless particles in quantum electrodynamics.
In this presentation, after a very simplified (an experimentalist view point!) introduction to the concepts of topology in solids, I will make an overview of our experimental results obtained by Terahertz/Mid-Infrared magneto-spectroscopy, on topological phase transitions driven by temperature in HgCdTe-based QWs [5, 6] and bulk films [7]. These transitions are accompanied with the appearance of 2D and 3D massless electrons called Dirac and Kane fermions, respectively. I will then briefly discuss the perspectives of our Montpellier group on Terahertz magneto-spectroscopy, such as Landau emission [8] and electron spin resonances.

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[3] M. Orlita, D. M. Basko, M. S. Zholudev, F. Teppe, W. Knap, V. I. Gavrilenko, N. N. Mikhailov, S. A. Dvoretskii, P. Neugebauer, C. Faugeras, A-L. Barra, G. Martinez & M. Potemski, Nature Physics 10, 233 (2014).
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[5] M. Marcinkiewicz, S. Ruffenach, S.S. Krishtopenko, A.M. Kadykov, C. Consejo, D. But, W. Knap, A. V. Ikonnikov, K.E. Spirin, S.V. Morozov, V.I. Gavrilenko, N.N. Mikhailov, S.A. Dvoretskii, F. Teppe; Phys. Rev. B. 96, 035405 (2017)
[6] A. M. Kadykov, S. S. Krishtopenko, B. Jouault, W. Desrat, W. Knap, S. Ruffenach, C. Consejo, J. Torres, S. V. Morozov, N. N. Mikhailov, S. A. Dvoretskii, and F. Teppe; Phys. Rev. Lett., 120, 086401 (2018)
[7] F. Teppe, M. Marcinkiewicz, S.S. Krishtopenko, S. Ruffenach, C. Consejo, A.M. Kadykov, W. Desrat, D. But, W. Knap, J. Ludwig, S. Moon, D. Smirnov, M. Orlita, Z. Jiang, S.V. Morozov, V.I. Gavrilenko, N.N. Mikhailov, S.A. Dvoretskii; Nature Commun. 7, 12576 (2016), doi:10.1038/ncomms12576
[8] D. B. But, M. Mittendorff, C. Consejo, F. Teppe, N. N.