Photoinduced Elastic Cooperative effect
This research aims at thorough understanding, and ultimately the control, of “Photo-induced elastic cooperativity in bi-stable volume-changing materials”. Unprecedented opportunities have emerged for impacting macroscopic states of materials with a femtosecond (fs) laser pulse, allowing to reach another electronic and/or structural order, thereby directing material functionality. The field of photo-induced phase transformations proliferates rapidly on many and diverse directions, from the melting of charge and/or spin order in electron correlated materials to molecular switching in the solid state.
Our investigations bring the photo-switching of materials from a new perspective, different from the common approach focused on electron and optical phonon dynamics at ultrafast timescales. Instead, we focus on crystal deformations occurring on the acoustic timescale. This is determined by the speed of sound and the size of the studied system, so generally slower, but also ultrafast when nano-scale materials are dealt with. On the one hand, elastically driven cooperative response during the propagation of a non-linear coherent strain wave coupled to the order parameter field has been recently reported by our group in a volume-changing material.
The medium exerts positive feedback which significantly amplifies the transformation ratio and extends the lifetime of the photo-induced state. On the other hand, a severe limitation to technological applications has been thus far the transient nature of photo-induced states, very often not surviving the fast relaxation of excited electrons and coherent (optical) phonons. It is of paramount importance from the fundamental standpoint, as well as for the control of non-volatile information and energy storage, to explore how the states induced by an ultra-short laser pulse can persist.
A promising route is the stabilization of the non-equilibrium macroscopic states by controllably generating the crystal deformation, such as volume change in thermodynamically bi-stable regime. The establishment of the macroscopic crystal deformation is necessary to attain a switched state that is robust against the thermal noise of environment. The main goal of this research is to investigate the underlying elastic cooperative mechanisms, and ultimately to master the non-volatile ultra-fast material switching.
Ultrafast non-thermal laser excitation of gigahertz longitudinal and shear acoustic waves in spin-crossover molecular crystals [Fe(PM–AzA)2(NCS)2]
T. Parpiiev, M. Servol, M. Lorenc, I. Chaban, R. Lefort, E. Collet, H. Cailleau, P. Ruello, N. Daro, G. Chastanet, T. Pezeril,
Appl. Phys. Lett. 111 (2017) 151901 - doi : /10.1063/1.4996538
Theoretical approach for elastically driven cooperative switching of spin-crossover compounds impacted by an ultrashort laser pulse
C. Enachescu, L. Stoleriu, M. Nishino, S. Miyashita, A. Stancu, M. Lorenc, R. Bertoni, H. Cailleau, E. Collet,
Phys. Rev. B 95 (2017) 224107 - doi : /10.1103/PhysRevB.95.224107
Elastically driven cooperative response of a molecular material impacted by a laser pulse
R. Bertoni, M. Lorenc, H. Cailleau, A. Tissot, J. Laisney, M. L. Boillot, L. Stoleriu, A. Stancu, C. Enachescu, E. Collet,
Nature Mater. 15 (2016) 606 - doi : /10.1038/nmat4606