Catégorie : Collaborations

Abstract : In organic semiconductors, bi-exciton states are key intermediates in carrier-multiplication and exciton annihilation. Of particular recent interest is the spin-2 (quintet) bi-exciton. Comprised of two triplet excitons, the bi-exciton can be formed by singlet fission (the formation of two triplet excitons from one singlet state) or by triplet-triplet annihilation (the reverse process). Of interest for photovoltaics and photocatalysis, the wavefunction of these optically dark bi-excitons is difficult to probe and predict. However, the local geometry of the pair-state is imprinted in the fine structure of its spin Hamiltonian. To access the fine structure of the quintet-state we develop and deploy broadband optically detected magnetic resonance (0-9 GHz). Here we correlate the experimentally extracted spin structure with the molecular crystal structure to identify the specific molecular pairings on which the bi-exciton state resides.

K. M. M Yunusova 1 S. L. L Bayliss 1 T. Chanelière 2, 3 V. Derkach 4 J. E. E Anthony 5 Alexei Chepelianskii 1 L. R. R Weiss 6
1 LPS – Laboratoire de Physique des Solides
2 NPSC – Nanophysique et Semiconducteurs
NEEL – Institut Néel
3 LAC – Laboratoire Aimé Cotton
4 Usikov’s Institute for Radiophysics and Electronics
5 University of Kentucky
6 Cavendish Laboratory

Abstract : We present a detailed numerical study of multi-component colloidal gels interacting sterically and obtained by arrested phase separation. Under deformation, we found that the interplay between the different intertwined networks is key. Increasing the number of component leads to softer solids that can accomodate progressively larger strain before yielding. The simulations highlight how this is the direct consequence of the purely repulsive interactions between the different components, which end up enhancing the linear response of the material. Our work {provides new insight into mechanisms at play for controlling the material properties and open the road to new design principles for} soft composite solids

Claudia Ferreiro-Cordova Mehdi Bouzid 1 Emanuela del Gado Giuseppe Foffi 2 Claudia Ferreiro-Córdova
1 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
2 LPS – Laboratoire de Physique des Solides

Adrien Devolder 1 Eliane Luc-Koenig 1 Osman Atabek 2 Michèle Desouter-Lecomte 3 Olivier Dulieu 1
1 LAC – Laboratoire Aimé Cotton
2 ISMO – Institut des Sciences Moléculaires d’Orsay
3 LCP – Laboratoire de Chimie-Physique

Abstract : An electron optical column has been designed for High Resolution Electron Energy Loss Microscopy (HREELM). The column is composed of electron lenses and a beam separator that are placed between an electron source based on a laser excited cesium atom beam and a time-of-flight (ToF) spectrometer or a hemispherical analyzer (HSA). The instrument will be able to perform full field low energy electron imaging of surfaces with sub-micron spatial resolution and meV energy resolution necessary for the analysis of local vibrational spectra. Thus, noncontact, real space mapping of microscopic variations in vibrational levels will be made possible. A second imaging mode will allow for the mapping of the phonon dispersion relations from microscopic regions defined by an appropriate field aperture.

Marian Mankos 1 Khashayar Shadman 1 Raphaël Hahn 2 Yan Picard 2 Daniel Comparat 2 Olena Fedchenko 3 Gerd Schönhense 3 Lionel Amiaud 4 Anne Lafosse 4 Nick Barrett 5
1 Electron Optica Inc.
2 LAC – Laboratoire Aimé Cotton
3 Institut für Physik [Mainz]
4 ISMO – Institut des Sciences Moléculaires d’Orsay
5 LENSIS – Laboratoire d’Etude des NanoStructures et Imagerie de Surface
SPEC – UMR3680 – Service de physique de l’état condensé, IRAMIS – Institut Rayonnement Matière de Saclay

Abstract : We study the propagation and storage of a quantum field using ultranarrow coherent population oscillations (CPOs) in a-type atomic medium. The predictions for classical fields are checked experimentally in a vapor at room temperature. We derive the evolution of its squeezing spectrum in the presence of a large classical pump field which enables CPOs to exist. We show that the spontaneous emission of the residual population pumped into the excited state progressively destroys the quantum noise properties of the quantum field along propagation. The output quantum field therefore tends to be a coherent state, discarding the possibility to store quantum states of light with CPO.

F. Bretenaker 1 F. Goldfarb 1 E. Brion 1, 2 Neveu Pascal 3
1 LAC – Laboratoire Aimé Cotton
2 LCAR – Laboratoire Collisions Agrégats Réactivité
3 LuMIn – Laboratoire Lumière, Matière et Interfaces

C. Lopez 1 A. Trimeche 2 D. Comparat 3 Y.J. Picard 3
1 LuMIn – Laboratoire Lumière, Matière et Interfaces
2 SYRTE – Systèmes de Référence Temps Espace
3 LAC – Laboratoire Aimé Cotton

Abstract : Hybrid organic-inorganic perovskites have become one of the most promising low-cost alternatives to traditional semiconductors in the field of photovoltaics and light emitting devices. It combines both attractive features of organic and inorganic materials within a single composite, for instance with excellent electronic properties. We used x-ray diffraction to reveal a sub-structure within CH 3 NH 3 PbI 3 single crystals. We could observe the presence of additional peaks with a square symmetry in several monocrystalline samples. We discuss these results in terms of two different models: a superstructure modulated in two in-plane orthogonal directions, and a model with tilted domains with a shallow angle of ~0.6°. In both cases, the modulated or tilted domains appear in regions with small lattice expansion. We show that this last model appears to be the most likely to explain our observations.

V.L.R. Jacques 1 A Gallo-Frantz 1 Antonio Tejeda 1 D Le Bolloc’h 1 Ferdinand Lédée 2 Gaëlle Trippé-Allard 2 Damien Garrot 3 Pierre Fertey 4 Emmanuelle Deleporte 2 Olivier Plantevin 5
1 LPS – Laboratoire de Physique des Solides
2 LAC – Laboratoire Aimé Cotton
3 GEMAC – Groupe d’Etude de la Matière Condensée
4 SSOLEIL – Synchrotron SOLEIL
5 CSNSM – Centre de Sciences Nucléaires et de Sciences de la Matière

Adama Creppy 1 Eric Clément 2 Carine Douarche 3 Maria Veronica d’Angelo 4 Harold Auradou 5
1 CNRS – Centre National de la Recherche Scientifique
2 PMMH – Physique et mécanique des milieux hétérogenes (UMR 7636)
3 LPS – Laboratoire de Physique des Solides
4 GMP – Grupo de Medios Porosos [Buenos Aires]
5 FAST – Fluides, automatique, systèmes thermiques

Abstract : Predicting the flow of non-Newtonian fluids in a porous structure is still a challenging issue due to the interplay between the microscopic disorder and the nonlinear rheology. In this Letter, we study the case of a yield stress fluid in a two-dimensional structure. Thanks to an efficient optimization algorithm, we show that the system undergoes a continuous phase transition in the behavior of the flow, controlled by the applied pressure difference. In analogy with studies of plastic depinning of vortex lattices in high−Tc superconductors, we characterize the nonlinearity of the flow curve and relate it to the change in the geometry of the open channels. In particular, close to the transition, a universal scale-free distribution of the channel length is observed and explained theoretically via a mapping to the Kardar-Parisi-Zhang equation.

Chen Liu 1 Andrea de Luca 2 Alberto Rosso 3 Laurent Talon 1
1 FAST – Fluides, automatique, systèmes thermiques
2 Rudolf Peierls Center for Theoretical Physics
3 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques

S. Brazovskii 1 N. Kirova 2
1 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
2 LPS – Laboratoire de Physique des Solides