Dynamical Quantum Properties of Phonons in Crystals

晶体中声子的动态量子特性

• 批准号: 417259631
• 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: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/417259631?language=en
• 关键词: Dynamical; Quantum; Properties; Phonons; Crystals

The present proposal aims at a combined experimental and theoretical study of the dynamical quantum properties of phonons in crystals. The joint experimental activities in Berlin (Michael Woerner) and theoretical calculations in Luxembourg (Alexandre Tkatchenko) aim at understanding fundamental microscopic mechanisms which underlie ultrafast atomic motions and electronic charge redistribution processes in crystalline matter for which quantum properties of phonons play a significant role. Experiments and theory will focus on coherent time-dependent processes of phonons. One part of the planned activities focuses on the coherent manipulation and fully phase-resolved detection of the density matrix of multi-phonon modes in crystals using a combination of coherent n-th-order Raman excitations and coherent THz emission which allows for exciting and probing "non-classical" states in the density matrix of multi-phonon modes. Another scientific goal of this proposal is the detailed spatio-temporal characterization (with atomic length and time resolution) of the soft mode phonons in ferroelectrics and molecular crystals. In contrast to "conventional" optical phonons in crystals soft modes have a pronounced hybrid character of nuclear motions and electronic charge relocations. Multi-dimensional terahertz spectroscopy and femtosecond x-ray diffraction are the main experimental techniques of the project. Since the electronic contribution to soft-mode currents is by orders of magnitudes larger than that of the nuclei, the Born Oppenheimer approximation in a theoretical description of soft modes is no longer a good approximation because the expectation value of the kinetic energy of the nuclei contains significant inter-electronic potential surface terms. The theoretical part of this proposal which starts with a well-established background based on van der Waals inclusive density functional theory (DFT) will be explored and extended into a direction to study theoretically such "non-Born-Oppenheimer" effects of phonons crystals.

本文旨在对晶体中声子的动态量子特性进行实验和理论的结合研究。柏林（Michael Woerner）的联合实验活动和卢森堡（Alexandre Tkatchenko）的理论计算旨在了解晶体物质中超快原子运动和电子电荷再分配过程的基本微观机制，其中声子的量子特性起着重要作用。实验和理论将集中于声子的相干时间依赖过程。计划活动的一部分重点是利用相干n阶拉曼激发和相干太赫兹发射的组合对晶体中多声子模式密度矩阵的相干操纵和完全相位分辨探测，这允许在多声子模式密度矩阵中激发和探测“非经典”态。本提案的另一个科学目标是铁电体和分子晶体中软模声子的详细时空表征（原子长度和时间分辨率）。与晶体中的“传统”光学声子相比，软模式具有核运动和电子电荷重定位的明显混合特征。多维太赫兹光谱和飞秒x射线衍射是该项目的主要实验技术。由于电子对软模式电流的贡献比原子核的贡献大几个数量级，所以软模式理论描述中的玻恩·奥本海默近似不再是一个很好的近似，因为原子核动能的期望值包含了重要的电子间电位表面项。本方案的理论部分将从基于van der Waals包容性密度泛函理论（DFT）的完善背景出发，探索并扩展到理论研究声子晶体的“非born - oppenheimer”效应的方向。