Aperiodic crystals: structure, dynamics and electronic properties

非周期晶体是指具有长程有序但缺乏晶格周期性的材料。它们由无公度调制结构、无公度复合晶体和准晶组成。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已经取得了进展，但非周期有序对物理性质的影响在很大程度上仍然没有被探索。该项目的目的是全面了解非周期长程有序和物理性质之间的关系，特别是声子、相子和电子自由度之间的相互关系。事实上，相子模是具有非周期有序特征的类扩散激发，但其与晶格动力学和电子性质的相互关系仍未被很好地理解。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业知识的领先团队将共同专注于原子结构、动力学和相子模以及电子性质三个方面。通过对非周期系统不同族中的五个精选系统的研究，我们旨在对非周期有序有一个普遍的理解。我们将利用大规模设施的新可能性，并通过使用DFT方法或模型哈密顿数进行最先进的原子尺度模拟来补充实验研究。具体的体系是：(I)磷酸钨青铜，它形成了具有软声子模和相子激发的二维CDW系统；(Ii)Rb2ZnCl4作为无公度调制相的例子，其中，当调制从简谐到强非谐时，首次可以研究相子模；(Iii)无公度复合晶体[SR]1+x[TiS3]，表现出高的结构有序；(Iv)最近发现的二维十二方氧化物准晶，其中相子反转可以被原子分解；以及(V)蔡依型二元二十面体准晶家族。这个雄心勃勃的项目将汇集三个法国和三个德国专家团队的能力。六名博士密切合作，将解决这一具有挑战性的问题。博士生的交流，联合实验，以及六个法德专家小组在理论和结构模拟方面的密切合作，将允许采取连贯的方法，并确保涵盖非周期晶体所有方面的广泛专业知识。它将为非周期晶体及其特殊性质带来新的曙光，为离子导电、高温超导体、电子和热传输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.