Structure-Driven Electronic Properties and Topology in Low-Dimensional Materials

Florian Max Arnold

AutorIn

Florian Max Arnold

Titel

Structure-Driven Electronic Properties and Topology in Low-Dimensional Materials

Zitierfähige Url:

https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-1014661

Übersetzter Titel (DE)

Strukturbestimmte elektronische Eigenschaften und Topologie in niedrigdimensionalen Materialien

Erstveröffentlichung

2026

Datum der Einreichung

26.06.2025

Datum der Verteidigung

08.12.2025

Abstract (EN)

Low-dimensional materials exhibit characteristics that can substantially differ from their bulk counterparts. A detailed understanding of the intricate relationship between atomic structure and material properties is essential to fully harness their potential. In this dissertation, I explore such structure-property relationships in two exemplary low-dimensional systems. The first is bilayer MoS2, where the introduction of an interlayer twist with a tunable twist angle θ induces the formation of moiré patterns. The second are zigzag graphene nano-ribbons (ZGNRs), where edge defects are introduced at the zigzag edge, which act as structural perturbations of the π-system. This work elucidates how these structural features govern the properties of the respective system. In the first part of the thesis, the effects of twistronics in bilayer MoS2 are shown. It is a semiconductor with a θ-dependent indirect band gap. Analysis of the local electronic properties reveals the formation of a moiré potential and charge carrier localization. These effects lead to the emergence of superlattice bands with honeycomb and kagome symmetry in the top valence bands. The superlattice features are robust at small θ with the bands becoming increasingly flat. Fitted model Hamiltonians enable extrapolation to θ→0° and θ→60°, predicting the emergence of super-heavy holes. The second part of the thesis focuses on edge engineering in cove- and gulf-edged ZGNRs. Four structural parameters label these systems unambiguously. Calculations using a tight-binding Hubbard model reveal spin-polarized states with antiferromagnetic ordering. Increasing the length of continuous zigzag edge segments in the ribbon stabilizes these states. All systems are semiconducting with band gaps between 0.5 and 1.5 eV, changing systematically with the structural parameters. The Z2 topological invariant follows simple empirical rules based on the structural parameters. These rules guide the construction of heterojunctions exhibiting localized topological junction states, which remain stable under structural perturbations. Overall, the results demonstrate how variations in the structural degrees of freedom enable a controlled modulation of electronic, magnetic, and topological features in low-dimensional materials. This work thus provides strategies for rational materials design that might guide future efforts toward device integration and quantum information technologies.

Freie Schlagwörter (EN)

Theoretical Chemistry, low-dimensional materials, electronic properties, topology, graphene nanoribbons

Klassifikation (DDC)

540

Klassifikation (RVK)

VE 9857

GutachterIn