Laboratoire de Physique des Solides, CNRS, University Paris-Sud, Université Paris-Saclay, 91405 Orsay, France.
Institute for Quantum Electronics, Physics Department, ETH Zürich, 8093 Zurich, Switzerland.
Nat Commun. 2017 Jan 9;8:13917. doi: 10.1038/ncomms13917.
The study of photoexcited strongly correlated materials is attracting growing interest since their rich phase diagram often translates into an equally rich out-of-equilibrium behaviour. With femtosecond optical pulses, electronic and lattice degrees of freedom can be transiently decoupled, giving the opportunity of stabilizing new states inaccessible by quasi-adiabatic pathways. Here we show that the prototype Mott-Hubbard material VO presents a transient non-thermal phase developing immediately after ultrafast photoexcitation and lasting few picoseconds. For both the insulating and the metallic phase, the formation of the transient configuration is triggered by the excitation of electrons into the bonding a orbital, and is then stabilized by a lattice distortion characterized by a hardening of the A coherent phonon, in stark contrast with the softening observed upon heating. Our results show the importance of selective electron-lattice interplay for the ultrafast control of material parameters, and are relevant for the optical manipulation of strongly correlated systems.
光激发强关联材料的研究越来越受到关注，因为它们丰富的相图通常转化为同样丰富的非平衡行为。飞秒光学脉冲可以瞬时解耦电子和晶格自由度，为稳定通过准绝热途径无法达到的新状态提供了机会。在这里，我们表明，原型莫特-哈伯德材料 VO 在超快光激发后立即出现瞬态非热相，并持续数皮秒。对于绝缘相和金属相，瞬态结构的形成都是由电子激发到成键 a 轨道引发的，然后通过晶格畸变稳定下来，其特征是 A 声子的软化，这与加热时观察到的软化形成鲜明对比。我们的结果表明，对于材料参数的超快控制，电子-晶格相互作用的选择性非常重要，这对于强关联系统的光学操控也具有重要意义。
