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Electron and phonon ultrafast dynamic

Electron and phonon ultrafast dynamic in solid exhibiting exotic coupling between charge, spin and structure


  • Vincent Juvé
  • Gwenaëlle Vaudel
  • Thomas Pezeril
  • Mathieu Edely,
  • Brice Arnaud,
  • Rémi Busselez,
  • Pascal Ruello.
  • Coll. B. Dkhil, C. Paillard, SPMS Centrale Supelec, J. Szade, K. Balin, Institute of Physics, Katowice (Poland). Laboratoire International Associé France-Japon (LIA-IM-LED)

Ultrafast photostriction in ferroelectrics and multiferroics

The control of the photoinduced coherent acoustic phonon in ferroelectric and multiferroic compounds have been investigated in order to investigate the electron-phonon coupling and the coherent acoustic phonon detection processes. This research has permitted to reveal an original ultrafast optical-light mode conversion in BiFeO3 and LiNbO3. We have shown that it was possible to switch the light polarization from the ordinary to the extraordinary component (and vice-versa) with coherent acoustic phonon and this, up to hundreds of GHz (10ps). This mechanism is based on the modulation of the birefringence of the uniaxial crystal (BiFeO3, LiNbO3) induced, through the acousto-optic effect, by the coherent acoustic phonons (left panel in the figure below) [1]. This work has been selected by INP CNRS as a “highlight” [2]. This research is still going on with a focus on new possible way to generate acoustic phonon [3] (transformation of light energy into mechanical energy) with an ANR project UP-DOWN (IMMM leader) that has started in October 2018. The extension of the coupling between coherent acoustic phonons with the magnetic order and in particular with antiferromagnons will be investigated in the ANR SANTA (SPEC-CEA Leader) that has started in October 2018 as well.


Ultrafast light-mode conversion in birefringent ferrolectric materialsUltrafast electron and phonon dynamics in Topological insulators

Related papers
  • Ultrafast acousto-optic mode conversion in optically birefringent ferroelectrics, Mariusz Lejman, Gwenaelle Vaudel, Ingrid C Infante, Ievgeniia Chaban, Thomas Pezeril, Mathieu Edely, Guillaume F Nataf, Mael Guennou, Jens Kreisel, Vitalyi E Gusev, Brahim Dkhil, Pascal Ruello, Nature comm. 7, 12345 (2016)
  • Photothermal optomechanics, P Ruello, Nature Photonics 10 (11), 692 (2016).

Ultrafast electron and phonon dynamics in topological insulators

In this work we have investigated ultrathin films of topological insulator (4-15nm). We have first studied the influence of the substrate and the microstructure (single versus polycrystalline structure on the femtosecond pulse-induced electron and phonon dynamics. While the optical phonons (zero group velocity) have frequency and damping dynamics nearly unaffected, the acoustic phonon signature (propagating wave) is clearly different revealing the importance of acoustic phonon scattering on grains boundaries and at interface between the nanometric film and the substrate [1]. In a second study, we have in particular measured the dynamic of hot carriers in Bi2Te3 compound and have shown the existence of a strong quantum confinement appearing for thickness as thin as 5-6nm. A dramatic enhancement of the hot carriers relaxation is observed (right panel in the figure above). Such quantum confinement is also revealed in a thickness dependence of the process of generation of coherent acoustic phonons and in the anomalous damping of a Raman active mode A1g mode, together with a slight A1g mode softening. These phenomena evidence a drastic evolution of the electron-phonon coupling in a highly confined system. We have proposed with a simple model, that the band gap increases with decreasing the thickness is an indication of the increase of the electron-longitudinal acoustic phonon deformation potential. A more advanced theoretical work is now required to extract a more precise microscopic picture. Nevertheless, these experimental results are important to tailor the proper thickness of such material for future integration in more complex devices where for example spin-to-charge conversion will be investigated.

Related papers
  • Ultrafast light-induced coherent optical and acoustic phonons in few quintuple layers of the topological insulator Bi2Te3, M Weis, K Balin, R Rapacz, A Nowak, M Lejman, J Szade, P Ruello, Physical Review B 92 (1), 014301 (2015)
  • Quantum size effect on charges and phonons ultrafast dynamics in atomically controlled nanolayers of topological insulators Bi2Te3, M. Weis, B Wilk, G Vaudel, K. Balin, R. Rapacz, A Bulou, B Arnaud, J Szade, P Ruello, Sci. Rep. 7, 13782 (2017)
  • French-Polish project, Bourse Ambassade de France (M. Weis), thèse co-tutelle (Le Mans, Insttut de Physique Katowice).
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