Mariette C, Lorenc M, Cailleau H, Collet E, Guérin L, Volte A, Trzop E, Bertoni R, Dong X, Lépine B, Hernandez O, Janod E, Cario L, Ta Phuoc V, Ohkoshi S, Tokoro H, Patthey L, Babic A, Usov I, Ozerov D, Sala L, Ebner S, Böhler P, Keller A, Oggenfuss A, Zmofing T, Redford S, Vetter S, Follath R, Juranic P, Schreiber A, Beaud P, Esposito V, Deng Y, Ingold G, Chergui M, Mancini G F, Mankowsky R, Svetina C, Zerdane S, Mozzanica A, Bosak A, Wulff M, Levantino M, Lemke H, Cammarata M
Univ Rennes, CNRS, IPR (Institut de Physique de Rennes)-UMR 6251, Rennes, France.
Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes)-UMR 6226, Rennes, France.
Nat Commun. 2021 Feb 23;12(1):1239. doi: 10.1038/s41467-021-21316-y.
One of the main challenges in ultrafast material science is to trigger phase transitions with short pulses of light. Here we show how strain waves, launched by electronic and structural precursor phenomena, determine a coherent macroscopic transformation pathway for the semiconducting-to-metal transition in bistable TiO nanocrystals. Employing femtosecond powder X-ray diffraction, we measure the lattice deformation in the phase transition as a function of time. We monitor the early intra-cell distortion around the light absorbing metal dimer and the long range deformations governed by acoustic waves propagating from the laser-exposed TiO surface. We developed a simplified elastic model demonstrating that picosecond switching in nanocrystals happens concomitantly with the propagating acoustic wavefront, several decades faster than thermal processes governed by heat diffusion.
超快材料科学中的主要挑战之一是用短光脉冲触发相变。在此，我们展示了由电子和结构前驱现象引发的应变波如何决定双稳态TiO纳米晶体从半导体到金属转变的相干宏观转变途径。利用飞秒粉末X射线衍射，我们测量了相变过程中晶格变形随时间的变化。我们监测了光吸收金属二聚体周围的早期晶胞内畸变以及由从激光照射的TiO表面传播的声波控制的长程变形。我们开发了一个简化的弹性模型，证明纳米晶体中的皮秒级开关与传播的声波波前同时发生，比由热扩散控制的热过程快几十倍。
