Ultrafast electronic charge redistribution processes in ionic crystals by femtosecond x-ray diffraction

通过飞秒 X 射线衍射研究离子晶体中的超快电子电荷重新分布过程

基本信息

批准号：
167525002
负责人：
Privatdozent Dr. Michael Wörner
金额：
--
依托单位：
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (MBI)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2010
资助国家：
德国
起止时间：
2009-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/167525002?language=en
关键词：
Ultrafast electronic charge redistribution processes

项目摘要

This project aims at understanding fundamental microscopic mechanisms which underlie ultrafast atomic motions and electronic charge redistribution processes in crystalline matter. The main scientific goal is a detailed spatial characterization (with atomic resolution) of the so called soft mode phonons in displacive ferroelectrics. The soft-mode is a complex interplay of ionic motions and inter-ionic electronic charge transfer processes. It is a sort of precursor of the phase transition with symmetry breaking changes of the electron density map which are inherent to coherent soft mode oscillations of ferroelectrics. The planned experiments aim at studying such changes using femtosecond x-ray diffraction by means of the rotation method. To this end, we will set up a new detector end station for the femtosecond x-ray rotation method which will allow for measuring up to 12 reflections simultaneously. Our planned experiments are based on a laser plasma source for hard x-ray pulses in combination with an intense terahertz source for applying strong electric field transients to the crystal. The proposed method will be sensitive to both field-driven anisotropic changes of the atomic positions within the unit cell, i.e. structural changes, and to electron transfer processes between various ions within the unit cell. A spatially resolved characterization of the soft-mode will clarify the interplay of electronic and ionic motions of this hybrid mode which is expected to lead in turn a better understanding of the ferro- to para-electric phase transition.A second series of experiments aims at electric field-induced quasi-instantaneous deformations of the electron density map in ionic crystals made of light elements (e.g. LiBH4, LiH, LiOH, NaBH4 etc.). The femtosecond x-ray rotation method on a multitude of equivalent reflections will give new experimental insights into ground state electron correlations of the materials. Furthermore, applying strong THz fields instead of optical fields to the crystals will give new insights in the relative contributions of spatial ionic shifts vs. electronic charge transfer to the macroscopic polarization.

该项目旨在理解基本的显微机制，这些机制是晶体物质中超快原子运动和电子电荷再分配过程的基础。主要的科学目标是详细的空间表征（具有原子分辨率），对位移铁电气中所谓的软模式声子进行了详细的空间表征。软模式是离子运动和离子电子电荷转移过程的复杂相互作用。它是相变的一种前体，具有对称性破坏电子密度图的变化，这是铁电的相干软模式振荡所固有的。计划的实验旨在通过旋转方法使用飞秒X射线衍射研究此类变化。为此，我们将为飞秒X射线旋转方法设置一个新的检测器终端站，该旋转方法将同时测量多达12个反射。我们计划的实验基于激光等离子体源，用于硬X射线脉冲，并结合强烈的Terahertz源，用于将强电场瞬变应用于晶体。所提出的方法将对单位电池内原子位置的现场驱动各向异性变化，即结构变化以及对单位电池中各种离子之间的电子传递过程的敏感。 A spatially resolved characterization of the soft-mode will clarify the interplay of electronic and ionic motions of this hybrid mode which is expected to lead in turn a better understanding of the ferro- to para-electric phase transition.A second series of experiments aims at electric field-induced quasi-instantaneous deformations of the electron density map in ionic crystals made of light elements (e.g. LiBH4, LiH, lioh，nabh4等）。众多等效反射上的飞秒X射线旋转方法将为材料的基态电子相关性提供新的实验见解。此外，将强的THZ场代替光场应用于晶体将提供有关空间离子移位相对贡献与电子电荷转移到宏观极化的相对贡献的新见解。