The Modelling of Photoinduced Phase Transitions in Anisotropic Media – MoPhaPho
Financed by the Romanian National Authority for Scientific Research, CNCS – UEFISCDI, project PN-III-3BM/2019
The research project described in the proposal will be conducted by investigators at the Excellence Center for Applied Research in Physics and Advanced Technologies (CARPATH) of the Faculty of Physics, “Alexandru Ioan Cuza” University (UAIC) from Iasi, Romania, and University of Rennes 1, France. This project will mix the expertise of the Collet group at IPR for photoinduced phase transition and ultrafast experimental studies and the expertise of the Enachescu group for modelling elastic coupling associated with these cooperative effects. These teams have complementary expertise: the group of University of Rennes 1 is one of the most important in the world with unique experimental facilities for the study of femtosecond phenomena in molecular materials, while the physicists at UAIC are internationally renowned for their models elaborated in order to characterize both spin crossover and magnetic materials and equally proposed new methods to analyze experimental data. The cooperation between the members of Rennes team and members of CARPATH started in 2012 and has been concretised up to now in a recent paper published in Nature Materials, at the heart of the present project.
Thanks to remarkable development of ultrafast techniques, operating on time scales faster than atomic motions or material reorganizations, new opportunities have emerged to impact the macroscopic state of a material, and thereby change its physical properties. Several experiments at the cutting edge of the laser and X-ray technologies have provided essential insights into real-time transformations of diverse materials, from the melting of charge and/or spin order in electron correlated systems to molecular switching in the solid state. Contrary to coherent optical phonons long under scrutiny, coherently propagating cell deformations over acoustic time-scale, have not benefited from the same surge of effort, in particular when the crystalline medium exerts positive feedback on the constituents. A severe limitation to photoinduced transformations triggered by a femtosecond laser pulse is their transient nature. A vast majority of reported experiments point to fast relaxation of excited electronic state and induced rearrangements of atoms inside unit cell, as factors prohibiting stabilisation. It is of paramount importance from the fundamental stand point, as well as for the control of non-volatile information, to explore whether induced crystal deformations have capacity to extend the lifetime of photoinduced states.
The goal of this project is to address the issue of the switching of materials by light pulse from the perspective of elastic cooperativity, notwithstanding its common perception related to electrons and optical phonons, we choose in this project to focus on spin-crossover systems where the phase transitions are driven by elastic interactions due to the swelling of photoswitched molecules.