Atomic-scale magnetic architectures with unconventional magnonic states

电子能带结构概念是凝聚态物理中最重要的概念之一。它是理解材料的物理和化学性质的一个基本概念。在固体中，由于表面(界面)平移对称性的破坏，可能会出现新的电子态，即表面(界面)态。在所谓的拓扑体中，在某些情况下，这些状态是拓扑保护的。拓扑保护态的概念并不限于费米子准粒子。类似地，集体玻色子激发，如声子、等离子体激子和磁子，也可以表现出非传统的表面(界面)态，这些表面(界面)态受到拓扑保护。由于其独特的性质，拓扑保护态可用于自旋电子学或磁子学的实际应用。在这个项目中，通过研究原子结构的铁磁金属外延层的模型系统，我们的目的是在层状结构中引入磁子表面(界面)态的概念及其可能的拓扑保护。为此，我们计划研究在HCP(0001)堆积中设计的层状铁磁体。首先，我们想了解这些结构中磁子表面态和界面态的物理。我们将利用自旋极化的高分辨电子能量损失谱来探测具有不同原子层顺序和层数的原子设计的层状体系中的磁子能带结构。然后，我们将仔细研究这种结构中的能带形成。我们将根据磁子带的真实空间局部化和拓扑来确定它们的起源，并对每个带的起源及其拓扑性质提供新的见解。

The concept of electronic band structure is one of the most important concepts in condensed-matter physics. It is an essential concept to understand both the physical and chemical properties of materials. In a solid, due to the broken translation symmetry at the surface (interface) new electronic states may appear, i.e., the surface (interface) states. In the so-called topological solids and under some circumstances, these states are topologically protected. The concept of topologically protected states is not limited to the fermionic quasiparticles. Similarly, the collective bosonic excitations e.g., phonons, plasmon, and magnons can also exhibit unconventional surface (interface) states, which are topologically protected. Owing to their unique properties, topologically protected states may be utilized for practical applications in spintronic or magnonic devices. In this project, by investigating model systems of atomically architectured epitaxial layers of ferromagnetic metals, we aim to introduce the concept of magnonic surface (interface) states and their possible topological protection in layered structures. For that, we plan to investigate layered ferromagnets designed in hcp(0001) stacking. We would like to, first, understand the physics of magnonic surface and interface states in these structures. We will probe the magnonic band structure in atomically designed layered systems with different sequences and number of atomic layers by means of spin-polarized high-resolution electron energy-loss spectroscopy. We will then carefully investigate the band formation in such structures. We shall identify the origin of the magnonic bands with respect to their real space localization and topology and provide new insights into the origin of each band and its topological nature.