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Elastically driven cooperative response of a molecular material impacted by a laser pulse


Photoinduced phase transformations1,2 occur when a laser pulse impacts a material, thereby transforming its electronic and/or structural orders, consequently affecting the functionalities3,4,5,6,7. The transient nature of photoinduced states has thus far severely limited the scope of applications. It is of paramount importance to explore whether structural feedback during the solid deformation has the capacity to amplify and stabilize photoinduced transformations. Contrary to coherent optical phonons, which have long been under scrutiny8,9,10, coherently propagating cell deformations over acoustic timescales11,12,13,14 have not been explored to a similar degree, particularly with respect to cooperative elastic interactions. Herein we demonstrate, experimentally and theoretically, a self-amplified responsiveness in a spin-crossover material15 during its delayed volume expansion. The cooperative response at the material scale prevails above a threshold excitation, significantly extending the lifetime of photoinduced states. Such elastically driven cooperativity triggered by a light pulse offers an efficient route towards the generation and stabilization of photoinduced phases in many volume-changing materials.

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Figure 1: Response to femtosecond laser excitation of LS crystals of different sizes.
Figure 2: Photoresponse of nanocrystals to excitation density.
Figure 3: Monte Carlo simulations with the mechanoelastic model.
Figure 4: Schematics of the mechanism.


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This work was supported by the Institut Universitaire de France, Rennes Métropole, Région Bretagne (CREATE 4146), ANR (ANR-13-BS04-0002) and Europe (FEDER). C.E. thanks CNCS-UEFISCDI Romania (grant number PN-II-RU-TE-2014-4-0987).

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Authors and Affiliations



E.C. and M.L. conceived and coordinated the project. R.B. performed time-resolved optical measurements and analysed the data. A.T., J.L. and M.-L.B. grew and prepared the samples. L.S., A.S. and C.E. extended the mechanoelastic model and performed Monte Carlo simulations. E.C., H.C., M.L., R.B. and C.E. proposed the physical picture and wrote the paper. All authors contributed to discussions and gave comments on the manuscript.

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Correspondence to Maciej Lorenc or Eric Collet.

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The authors declare no competing financial interests.

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Bertoni, R., Lorenc, M., Cailleau, H. et al. Elastically driven cooperative response of a molecular material impacted by a laser pulse. Nature Mater 15, 606–610 (2016).

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