Quantum Low Dimensional Materials and their Topological and Collective Properties

量子材料使我们能够探索复杂过程的迷人世界。材料作为各种粒子或准粒子的宿主，并定义了粒子的性质及其相互作用的规则。例如，在单层石墨烯中，电子和声子除了被限制在二维空间之外，还具有特殊的性质，其中低能电子具有特殊的线性色散（狄拉克费米子），并且磁场中的电子激发可以具有分数电荷和非常规统计。石墨烯中的声子也很特别。它们是石墨烯高导热性的原因，一些研究人员认为这与声子的流体动力学传输有关（电子也表现出类似的行为）。对于声子来说，这与集体兴奋的第二个声音有关。许多这些有趣的特性都是主体材料二维特性的结果，石墨烯通常被认为是平面的，但是可以弯曲石墨烯，甚至改变其几何拓扑结构，例如通过在单个石墨烯层中形成Möbius环。这种局部宿主环境的新几何形状将如何影响电子、声子甚至自旋等粒子的性质？在本研究项目中，我们将重点关注这些低维系统中的不同相互作用及其与拓扑和无序的相互作用。特别是，我们还将更详细地探讨石墨烯中的声子工程领域。最近在石墨烯中合成了第一个同位素超晶格，可以说我们已经在实验上开辟了这一新的研究领域，现在我们已经准备好探索这个新的宇宙。其基本思想是通过在石墨烯晶体合成过程中控制碳13和碳12原子的位置来创造人工同位素结构。这是通过在石墨烯的化学气相沉积中使用相应的同位素纯甲烷气体来实现的。利用这种技术，我们能够合成周期低至6nm的同位素超晶格，在拉曼光谱中显示出一种新的石墨烯声子色散，具有引人注目的新特征。这有有趣的潜在应用，由于降低了热导率，这将导致一个非常高的塞贝克系数和热电应用的高品质数字。这项研究计划的一部分是测量这些输运性质作为同位素周期性的函数。在仪器方面，我们将通过拉曼光谱将超分辨率技术应用于化学物质的高空间分辨率成像，这将把这项技术推向新的未知领域，为先进的材料表征开辟新的途径。

Quantum Materials allow us to explore a fascinating world of complex processes. The material acts as a host to various particles or quasi particles and defines the properties of the particles and their rules of interactions. For instance, in single layer graphene, in addition to being confined in two dimensions, electrons and phonons have special properties, where the low energy electrons have a peculiar linear dispersion (Dirac fermions) and where electronic excitations in a magnetic field can have fractional charges and unconventional statistics. Phonons in graphene are also very special. They are responsible for the very high thermal conductivity of graphene and some researchers have argued that this is related to the hydrodynamic transport of phonons (electrons show similar behavior too). For phonons this is related to the second sound of collective excitations. Many of these interesting properties are a consequence of the two-dimensional nature of the host material, where graphene is usually thought of as planar, but it is possible to curve graphene and even change its geometric topology like by forming a Möbius ring out of a single graphene layer. How would this new geometry of the local host environment impact the properties of particles like electrons and phonons or even spins? In this research program we will focus on the different interactions in these low-dimensional systems and their interplay with topology and disorder.  In particular, we will also explore in more detail the field of phonon engineering in graphene. Having arguably opened experimentally this new field of research by recently synthesizing the first isotope superlattices in graphene, we are now well positioned to explore this new Universe. The underlying idea is based on creating artificial isotope structures by controlling the position of the Carbon 13 and Carbon 12 atoms during the synthesis of graphene crystals. This is achieved by using the corresponding isotopic pure methane gases in the chemical vapor deposition of graphene. Using this technique, we were able to synthesize isotope superlattices with periods down to 6nm, which show a new graphene phonon dispersion with striking new features in the Raman spectrum. This has interesting potential applications due to the reduced thermal conductivity, which should lead to a very high Seebeck coefficient and a high figure of merit for thermoelectric applications. Part of this research program, is to measure these transport properties as a function of isotope periodicity. On the instrumentation side, we will apply super-resolution techniques to high spatial resolution imaging of chemical species via Raman spectroscopy, which will push this technique to new unexplored regime to open new pathways for advanced material characterizations.