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Ultrafast Phenomena

Ultrafast Phenomena

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

Researchers

  • Vivent 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)
  • http://www.cnrs.fr/inp/spip.php?article4895
  • Photothermal optomechanics, P Ruello, Nature Photonics 10 (11), 692 (2016).
Projects

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)
Projects
  • French-Polish project, Bourse Ambassade de France (M. Weis), thèse co-tutelle (Le Mans, Insttut de Physique Katowice).

Nonlinear acousto-magneto-plasmonics

Topological and nonlinear magneto-plasmonics

In functional magnetic nanostructures acoustic, magnetic and plasmonic excitations can co-exist and interact on nanometer spatial and ultrafast time scales.  Optical spectroscopy with femtosecond laser pulses highlights a variety of nonlinear and spatio-temporal dynamical phenomena, which are not only used to monitor individual excitations in real time, but also to study their mutual interaction mechanisms [1]. Hybrid metal-ferromagnet multilayer structures [2] of periodically patterned plasmonic thin films in various topological configurations [3] can display unique linear and nonlinear magneto-optical properties; some of them can be probed by magnetic second-harmonic (SH) generation. 

Nonlinear magneto-plasmonic experiments on metal-ferromagnet multilayer films exploit a significant dispersion of surface plasmon polaritons (SPPs) at fundamental and SH frequencies, which can be excited at different incidence angles in Kretschmann configuration using femtosecond laser pulses [1,2]. This angular dependence and magnetic control of second-order nonlinear-optical interactions at noble metal-ferromagnet interfaces enable the detailed study of phase-matching conditions governing the excitation of SPPs.

Periodic nanostructuring of magnetic thin films introduces new degrees of freedom in magneto-optical measurements allowing for the transition between optical gratings (large periodicity compared to optical wavelength) and metasurfaces (small periodicity) to be observed. As a first step in understanding of this new class of functional magneto-optical nanomaterials we have investigated the Wood’s diffraction anomaly on periodic arrays of nickel nanodimers. A periodic structure acting as a meta-surface at the fundamental frequency and as a diffraction grating at the double SH frequency has been identified using concepts of linear and nonlinear Wood’s anomalies [4].

Nonlinear magneto-plasmonics [1,2]

Topological plasmonics [3]

Researchers
  • Vivent Juvé
  • Gwenaëlle Vaudel
  • Vasily Temnov
  • D. Kuzmin, I. Bychkov (Chelyabinsk State University, CNRS-RFBR PRC partner university)
Related papers
  • [1] V.V. Temnov et al., J. Opt. 18, 093002 (2016)
  • [2] I. Razdolski et al., ACS Photonics 3, 179 (2016)
  • [3] D.A. Kuzmin et al., ACS Photonics 4, 1633 (2017); Nanophotonics 7, 597 (2018)
  • [4] M. Tran et al., Phys. Rev. B 98, 245425 (2018)
Projects

This research is by now currently supported by a Strategie Internationale “NNN-TELECOM” de la Region Pays de la Loire (2015-2019),  French-Russian CNRS-RFBR PRC “Acousto-magneto-plasmonics” (2017-2019), European COST action MP1403 “Nanoscale quantum optics”, the ITMO University St. Petersburg (Research professorship program 2019-2021).

Ultrafast acoustics and magneto-acoustics with surface acoustic waves

Optical spectroscopy with femtosecond laser pulses highlights a variety of nontrivial spatio-temporal dynamics, which are not only used to monitor individual excitations in real time, but also study interaction mechanisms between them, often observed in frequency mixing phenomena.   In acoustics and magnetism they are often dominated by parametric resonances, where system parameters are modulated at frequencies comparable to the natural oscillation frequencies, typically in the MHz-GHz range.

In recent experiments [1,2] the magnetization in a Ni/glass sample is excited by two distinct transient surface acoustic waves (denoted as SAW and SSLW, respectively, and recently quantified in time-resolved x-ray diffraction experiments [3]). Magnetic tuning of the FMR frequency in resonance to their SHG, sum- and difference frequencies demonstrates the full variety of frequency mixing phenomena [2]. In contrast to nonlinear optics, the frequency mixing is dominated by the parametric effect in the externally driven FMR oscillator. An analytical model based on the resonant enhancement of frequency-mixed signals explains the experimental observations [2]. The detailed understanding of magneto-interactions in nickel thin films motivates realistic concepts for acoustic magnetization switching at the nan-scale. For example, we have performed realistic modeling for nickel nanostructures to show that an elliptical nickel nanoparticle placed in a weak external magnetic field can be switched with small-amplitude pulses of surface acoustic waves [4].

Extending our theoretical modeling beyond the acoustically-driven FMR precession allows us to study intriguing interactions between ultrashort acoustic pulses and standing spin waves (exchange magnons) in thin ferromagnetic films. A practical application of these findings to magneto-elastic switching in bi-stable systems, i.e. nickel nanomagnets, is under way [4].

 

Parametric magneto-acoustic frequency mixing [2Elastic switching of nanomagnets [4]

Researchers
  • VasilyTemnov
  • V.S. Vlasov, A. Golov, L.N. Kotov (Syktyvkar State University, CNRS-RFBR PRC partner university)
  • D. Seletsky, A. Leitenstorfer (Konstanz University, ANR-DFG partner university)
Related papers
  • [1] J. Janusonis et al., Phys. Rev. B 94, 024415(2016)
  • [2] C.L. Chang et al., Phys. Rev. B 95, 060409 (2017)
  • [3] M. Sander et al., Phys. Rev. Lett. 119, 075901 (2017)
  • [4] V.S. Vlasov et al., Crystals (to appear in 2019)
Projects

This research is by now currently supported by a Strategie Internationale “NNN-TELECOM” de la Region Pays de la Loire (2015-2019),  French-Russian CNRS-RFBR PRC “Acousto-magneto-plasmonics” (2017-2019), French-German ANR-DFG “PPMI-NANO” (2015-2019), the ITMO University St. Petersburg (Research professorship program 2019-2021).

Ultrafast Acoustics

Researchers

  • Rémi Busselez

  • Thomas Pezeril

  • Gwenaëlle Vaudel

  • Vincent Juvé

  • Guillaume Brotons

  • Nicolas Delorme

  • Pascal Ruello

  • Coll. H. Piombini, P. Belleville CEA Le Ripault, V. Gusev, S. Raetz, N. Chigrev LAUM Le Mans Univ (Lmac Project). K. Nelson, C. Klieber (MIT, USA)

Vibrational properties of liquids and interfacial liquids

At Solid-Liquid interface, a drop of liquid film thickness towards nanoscale induces deep modifications of the liquid properties such as heat or particle transport, fluid rheology and lubrication. Among the properties impacted by the fluid size reduction and liquid-solid interface, the importance of the modifications in vibrational properties are actually scrutinized and debated. Despite this interest in interfacial liquids, experimental measures are not easily accessible at exceptions of Surface Force Apparatus and Atomic Force Microscopy techniques. We recently develop a home-built Time Dependant Brillouin Scattering permitting to reach the GHz dynamics range for liquids of thickness comprises between few microns to tenth of nanometers permitting to access to viscoelastic properties from the bulk liquids to thin films and may shed a new light on the comprehension of interfacial fluid properties.

TDBS measurements are also supported by molecular dynamics simulations which permits to bridge a gap between the length and time scales of both techniques and may relate modifications of macroscopic values such as viscoelastic properties to microscopic aspects.

 

TDBS spectra of glycerol at different temperaturesVelocity of longitudinal and transverse sound as a function of frequency obtained with molecular dynamics simulation of glycerol at different temperatures

Related papers
  • [1]I. Chaban, H. D. Shin, C. Klieber, R. Busselez, V. E. Gusev, K. A. Nelson and T. Pezeril, Time-domain Brillouin scattering for the determination of laser-induced temperature gradients in liquids, Review of Scientific Instruments, 2017, 88, 074904.
  • [2]R. Busselez, T. Pezeril and V. E. Gusev, Structural heterogeneities at the origin of acoustic and transport anomalies in glycerol glass-former, The Journal of Chemical Physics, 2014, 140, 234505.
Projects

Probing elasticity at the nanoscale

The ability to generate and to detect with femtosecond lasers coherent acoustic phonons with very high frequency (10-100s GHz) offers an unique possibility to directly measure the propagation speed of these acoustic phonons in nanostructures and then to investigate the elasticity [1]. Within this context, we have applied our method to probe the elasticity of different systems. First of all, we have studied assemblies of silica nanoparticles (10nm). These are the central element in advanced coating of many lenses in the French project Laser MégaJoule of CEA-DAM. The realization of coating with NPs assemblies permits to remove the coating quite often after each LaserMegaJoule Impact and to renew then the lenses. However, no advanced investigations of the mechanical properties of these coating were achieved up to now. This was our task. In this study, we have been able then to reveal the nature of the contact between nanoparticles (Van der Waals or Hydrogen, Covalent) directly by evaluating how fast the coherent acoustic phonon propagate within a thin film made of this nanoparticle (see figure below). The transformation of such bond (called hardening process) was realized by chemists of CEA. We have been then able to extract the characteristic elastic modulus of films as thin as 70nm (but the technique can be applied to thinner system) [2]. This research has been selected by CEA DAM as one of the 25 more important results in 2017 of research at CEA DAM.

We have also recently applied this method to detect a phase transition in thin films of the multiferroic compound BiFeO3. In particular, we are able to distinguish the transition from the rhombhedral to tetragonal phase by analyzing the values of the sound velocity measured in sub-micrometric films [3].

 

Left: principal of a pump-probe method on a thin film made of an assembly of nanoparticles. The pump laser can induced mechanical resonances of the film that in turn induce some periodic modulation in time on the optical reflectivity. The latter one is measured with the probe beam Typicall mechanical oscillations are shown on the right where the change of frequency of the two first eigenmode clearly indicate the modification of the nanoscontact strength.

Related papers
  • [1] Advances in applications of time-domain Brillouin scattering for nanoscale imaging, VE Gusev, P Ruello, Applied Physics Reviews 5 (3), 031101 (2018)
  • [2] Controlling the Nanocontact Nature and the Mechanical Properties of a Silica Nanoparticle Assembly, J Avice, C Boscher, G Vaudel, G Brotons, V Juvé, M Edely, C Méthivier, Vitalyi E Gusev, Philippe Belleville, Herve Piombini, Pascal Ruello The Journal of Physical Chemistry C 121 (42), 23769-23776 (2017)
  • [3] Evaluation of the structural phase transition in multiferroic (Bi1-x Prx)(Fe0.95 Mn0.05)O3 thin films by a multi-technique approach including picosecond laser ultrasonics,  Samuel Raetz, Alexey Lomonosov, Sergey Avanesyan, Nikolay Chigarev,  Elton de Lima Savi, Alain Bulou, Nicolas Delorme, Zheng Wen, Qiao Jin, Maju  Kuriakose, Anthony Rousseau, Gwenaëlle Vaudel, Pascal Ruello, Di Wu, Vitalyi  Gusev, in revision in Applied Sciences
Projects
  • Contrat CEA (2015-2018) avec Bourse cofinancé CEA-Région Pays de la Loire

Ultrafast terrahertz spectroscopy

Researchers

  • Gwenaëlle Vaudel
  • Vasily Temnov
  • Pascal Ruello
  • Thomas Pezeril
  • Vincent Juvé.
  • Coll. JY CHauleau, M. Viret, CEA-SPEC, J. Szade Institute of Physics Katowice (Poland), Laboratoire International Associé CNRS, France-Japon (LIA-IM-LED)

THz polarization modulation of visible light by THz pulses

Over the last decade, ultrafast Terahertz spectroscopy has gained tremendous attention thanks to the development of high-power ultrafast laser systems, which allowed generating intense single-cycle picosecond pulses of electric field at THz frequencies. Their relatively long optical cycle period (1 ps for 1 THz) and high electric field (from hundred of kV/cm to few MV/cm) provide a new tool for studying fundamental aspects of light-matter interactions. Field-resolved detection of ultra-short THz pulses is well known since many years and the most common technique is based on free-space electro-optic sampling. This leads to the polarization change of an optical pulse, which is detected by the polarization sensitive scheme, and to the field-resolved detection of a THz pulse. Here we evidenced efficient non-resonant and noncollinear χ(2)-type type light-matter interaction in femtoseconds polarization sensitive time-resolved optical measurements. Such nonlinear optical interaction of visible light and ultra-short THz pulses leads to THz modulation of visible light polarization in bulk LiNbO3 crystal. Theoretical simulations based on the wave propagation equation capture the physical processes underlying this nonlinear effect [1].

 

Left: A femtosecond optical pulse and a THz pulse, delayed in time respect to each other, are overlapping in a LiNbO3 crystal. Right: Non-resonant and noncollinear χ(2)-type light-matter interaction leads to a rotation Δθ of the optical pulse polarization at THz frequencies

Related papers
  • [1] V. Juvé, G. Vaudel, Z. Ollmann, J. Hebling, V. Temnov, V. Gusev and T. Pezeril, Optics Letters 43 (2018)
Projects

Ultrafast THz emission by spin to charge current conversion (ferroic materials and topological insulators)

 Topological insulators (Bi2Se3, Bi2Te3 etc…) are a new class of material, which is stated to be at the core of the next generation of electronics devices. Their structure consists of a bulk small bandgap insulator together with spin polarized surface states, which can lead to surface spin current. Studying and controlling the surface spin current is of interest for the scientific community. Using ultrafast THz spectroscopy, with photon energy smaller than the band gap, one can try to have access to the surface states dynamics and, thus, to the spin dynamics. High quality samples, which are well characterized of Bi2Te3, are provided by the University of Silesia in Poland [1].

 

Left: Simplified band structure of topological insulators, which consists of a combination of a small band gap together with spin-polarized Dirac cones. Right: Relative change of the transmission induced by a THz pulse (2 meV photon energy) measured with a 3.1 eV photon energy for a Bi2Te3 sample of 15nm thickness.

 

We also have started to investigate the emerging field related to spin-to-chareg conversion (vice-versa). spin bursts can be produced by direct excitation of hot electrons in a ferromagnetic layer triggered by a femtosecond laser pulse. During the relaxation processes the diffusion lifetime and mobility differ for majority and minority spin carriers, resulting in the emission of angular momentum on a timescale of picoseconds. This effect, combined with Inverse Spin Hall Effect in an adjacent non-magnetic layer (Pt), was recently used to make efficient THz generation devices [2]. Based on this principle, we have already carried out preliminary measurement with CoFeB on Pt by shining femtosecond laser pulses to inject spin current bursts. As the direction of spin current is determined by the magnetization of the Ferromagnetic, the mechanism provides an easy and efficient way of controlling the direction of spin torque with a small magnetic field. This project is part of the Santa ANR (2018-2021) lead by Michel Viret (CEA/SPEC) within which IMMM is involved (starting Oct 2018).

 

Left: Principle of the spin to charge current conversion leading to THz emission (taken from Seifert et al Nat. Phot. 2016). Right: Ultrafast THz emission measured by electro-optic sampling after ultrafast photoexcitation in a FeCoB(5nm)/Pt(3nm) sample. Reversing the external magnetic field leads to a change of sign of the THz electric field.

Related papers
  • [1] V. Juvé et al, in preparation
  • [2] T. S. Seifert, N. M. Tran, O. Gueckstock, S. M. Rouzegar, L. Nadvornik, S. Jaiswal, G. Jakob, V. V. Temnov, M. Münzenberg, M. Wolf, M. Kläui and T. Kampfrath. J. Phys. D Appl. Phys. (2018)
Projects

Simulation of ultrafast phenomena

Researchers

  • Brice Arnaud
  • Florent Calvayrac

Electron and phonon dynamics in photoexcited solids

Schematic view of relaxation processes in photoexcited silicon

Pump probe experiments like optical pump probe experiments, time resolved X-ray diffraction, or time resolved photoemission experiments are currently used to study electron and phonon dynamics in nanostructures on time scales ranging from a few femtoseconds to a few picoseconds.  Among the aforementioned techniques, optical pump probe experiments allow to study the coherent phonon generation mechanisms or even the possibility to demagnetize a sample with an ultrashort laser pulse. It is often difficult to interpret experimental results without resorting to models whose parameters can be inferred from ab-initio calculations. There are few calculations because of the need to describe non-equilibrium phenomenon occurring on different time scales and length scales. Nonetheless, ab-initio calculations combined with models already shed new light on ultrafast physics, especially on the coherent phonon generation, on the non thermal melting processes or on the energy transfer from the electronic degrees of freedom to the the vibrational degrees of freedoms.

 

Related papers
  • Isabel González Vallejo,  Geoffrey Gallé, Brice Arnaud, Shelley A. Scott,  Max G. Lagally,  Davide Boschetto, Pierre-Eugene Coulon,  Giancarlo Rizza,  Florent Houdellier,  David Le Bolloc’h,  and Jerome Faure, “Observation of large multiple scattering effects in ultrafast electron diffraction”, Phys. Rev. B 97, 054302 (2018).

TDDFT approaches to compute excited states of finite systems

The PW-TELEMAN project aims at developing an open source (under GPL3) and easy accessible package of real-time TDDFT libraries and codes, based on programs developed over the past 20 years in a Toulouse-Erlangen collaboration which spread to Le Mans and China via former students. At the time being no available code truly accounts for a complete non-adiabatic electron-ions coupling allowing a full follow-up of a whole dynamical scenario from early excitation (fs or sub-fs) to long time response (ps) of a given physical system. To the best of our knowledge, the Toulouse-Erlangen package is one of the single ones allowing such an investigation in a fully time-resolved manner. Still this package requires a strong effort of standardization and documentation and in order to make it more efficient and usable by external groups. More optimization is highly desirable to exploit the latest computer technology such as GPGPU and so to access the much more demanding tasks in organic molecules. It is the goal of the project to succeed in these two complementing directions.

The variety of potential applications is obvious. We mention in particular the very practical aspects concerning irradiation of biological molecules and radiation damage in materials. The plan is to develop our project in two complementing directions: first, implementation and tests of formal developments such as approximations to TDSIC/OEP methods, coupled with an exploration of various dynamical scenarios of increasing complexity (requiring ongoing optimization), starting with free molecules and clusters, turning to systems such as a chromophore cluster embedded in a matrix, ending with a coupled quantum mechanics/molecular mechanics hierarchical modeling of a biophysical problem made possible due to the expected increase in numerical performance and on the other hand standardization, documentation, and publication of a toolbox of routines which will be easily usable by other groups.

 

Benchmark of PW-Teleman code, Efficiency versus core number for differents architecture optimisation

Related papers
  • Calvayrac, Kullback-Leibler divergence as an estimate of reproducibility of numerical results, in: IEEE, 2015: pp. 1-5. DOI: 10.1109/NTMS.2015.7266501
Projects
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