Atomic-scale magnetic architectures with unconventional magnonic states

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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.