Effect of symmetry constraints on the topological properties of solid state systems

Gabriele Naselli

AutorIn

Gabriele Naselli

Titel

Effect of symmetry constraints on the topological properties of solid state systems

Zitierfähige Url:

https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-970999

Erstveröffentlichung

2025

Datum der Einreichung

27.11.2024

Datum der Verteidigung

09.05.2025

Abstract (EN)

Since the development of the tenfoldway, it has been widely recognized that local symmetries (such as chiral, time reversal, or particle hole symmetry) significantly influence the protection and characteristics of topological states within topological insulators. Furthermore, some types of topological insulators, such as weak topological insulators (WTIs) and antiferromagnetic topological insulators (AFTIs) have boundary states protected by lattice symmetries, in addition to the local ones. In this thesis we will explore new ways in which symmetries can influence the topological properties of topological insulators and Weyl semimetals. We will first explore the role of symmetries in the protection of new topological states in the presence of lattice defects. Even though, generally, lattice defects may obscure electronic topological features of real materials, recently it has been shown that they can act as a source of nontrivial topology, depending on their geometry and symmetries. In this thesis, we will study the effect of stacking faults on the electronic properties of weak topological insulators and show that, depending on the symmetry of the defect, the latter can host different novel topological states. We will then explore how the creation of a new topological phase can change the symmetries of the observable properties in a topological system. More specifically, we will study the effect of antiferromagnetic order in 3D topological insulators and show that the warping of the surface Dirac cone changes its symmetry from hexagonal to trigonal, when antiferromagnetic ordering is introduced in the system. The warping can be used as an alternative way to detect antiferromagnetic order in topological insulators. In the last part of the manuscript we will show that symmetries also play an important role in shaping the topological properties of gapless topological phases. For example, it is known that higher order topological degeneracy points, such as double Weyl nodes, require symmetry constraints for their protection. We will show that symmetry constrains not only stabilize high order degeneracy points but they can be used to observe multiple Weyl node merging processes in Weyl semimetals.

Freie Schlagwörter (EN)

Condensed matter physics, Topological Insulators, Weyl semimetals

Klassifikation (DDC)

530

Klassifikation (RVK)

UP 1200

GutachterIn