Aperiodic crystals: structure, dynamics and electronic properties

非周期晶体是具有长程有序但缺乏晶格周期性的材料。它们包括不相称调制结构、不相称复合晶体和准晶体。它们存在于从元素到蛋白质的各种系统中。尽管在理解它们迷人的结构方面取得了进展，但非周期顺序对物理性质的影响在很大程度上仍未被探索。该项目的目标是提供对非周期长程序与物理性质之间关系的全面理解，特别是声子、相子和电子自由度之间的相互关系。事实上，相模是具有非周期顺序特征的类扩散激励，但其与晶格动力学和电子性质的相互关系仍未得到很好的理解。为了超越现有的理解，需要像这里提议的那样共同努力。六个在非周期系统领域具有互补实验和理论专长的领先团队将共同关注原子结构，动力学和相模以及电子特性三个方面。通过对从不同的非周期系统族中选出的5个系统的研究，我们旨在对非周期序有一个广义的理解。我们将采用大规模设施的新可能性，并通过最先进的原子尺度模拟来补充实验研究，使用DFT方法或模型哈密顿量。具体体系有：(1)形成具有软声子模式和相位激发的二维CDW体系的磷酸钨青铜；（ii）以Rb2ZnCl4为例，首次研究了从谐波调制到强非谐波调制时的相位模式；（iii）不相称的复合晶体[Sr]1+x[TiS3]，结构有序；（iv）最近发现的二维十二角体氧化物准晶体，其中相位翻转可以原子分辨；(v) tsai型二元二十面体准晶族。这个雄心勃勃的项目将汇集三个法国和三个德国专家组的能力。六位博士将密切合作解决这一具有挑战性的问题。六个法德专家团队之间的博士生交流、联合实验以及与理论和结构模拟的密切合作将允许一个连贯的方法，并确保广泛的专业知识涵盖非周期晶体的各个方面。它将为非周期晶体及其特殊性质带来新的启示，也可能为离子传导、高tc超导体、电子和热输运以及热电材料等领域的新应用铺平道路。

Aperiodic crystals are materials that possess long-range order but lack lattice periodicity. They comprise incommensurately modulated structures, incommensurate composite crystals and quasicrystals. They are found in a large variety of systems, ranging from the elements to proteins. Although progress has been made in understanding their fascinating structures, the impact of aperiodic order on physical properties is still largely unexplored. The objective of the project is to provide a comprehensive understanding of the relationship between the aperiodic long-range order and physical properties, in particular the interrelation between phonon, phason, and electronic degrees of freedom. Indeed phason modes are diffusive-like excitations that are characteristic of aperiodic order, but whose interrelation with lattice dynamics and electronic properties is still not well understood. To go beyond the existing understanding, a joint effort is needed as proposed here. Six leading teams with complementary experimental and theoretical expertise in the field of aperiodic systems will together focus on the three aspects atomic structure, dynamics and phason modes, as well as electronic properties. Through a study of five well-chosen systems out of the different families of aperiodic systems, we aim at a generalized understanding of aperiodic order. We will employ the new possibilities of large-scale facilities and supplement the experimental study by state of the art atomic scale simulations, using either the DFT approach or model Hamiltonians. The specific systems are: (i) The phosphate tungsten bronzes that form two-dimensional CDW systems with soft phonon modes and phason excitations; (ii) Rb2ZnCl4 as an example of an incommensurately modulated phase, in which, for the first time, phason modes can be studied when the modulation goes from harmonic to strongly anharmonic; (iii) the incommensurate composite crystals [Sr]1+x[TiS3], exhibiting high structural order; (iv) recently discovered two-dimensional dodecagonal oxide quasicrystals, where phason flips can be atomically resolved; and (v) the Tsai-type binary icosahedral quasicrystal family. This ambitious project will gather the competences of three French and three German expert teams. Six PhDs working in close collaboration will tackle this challenging problem. The exchange of PhD students, the joint experiments, and the close cooperation with theory and structure simulations among six French-German expert teams will allow for a coherent approach and ensures broad expertise covering all aspects of aperiodic crystals. It will shine new light on aperiodic crystals and their specific properties that might pave the way also for new applications in fields such as ionic conduction, high-Tc superconductors, electronic and thermal transport, and thermoelectric materials.