Thesis defence T.Ö. Rosdahl: topological materials

25 March 2019 15:00 - Location: Aula, TU Delft - By: webredactie

Symmetries and Boundary Conditions of Topological Materials: General Theory and Applications. Promotor: Dr. A.R. Akhmerov (TNW).

Topology is the study of properties that are preserved under smooth deformations, such as stretching or bending, but destroyed by abrupt changes, like breaking or tearing. Some materials host electronic states at their edges as a consequence of the topology and sym- metry of the material Hamiltonian, which is a central object in the equations governing the quantum mechanical state of the material. Because of their topological character, these states are robust to perturbations, which makes them attractive for applications.

Knowledge of the symmetries of a Hamiltonian is crucial to understand its topological properties. We offer an algorithmic approach to Hamiltonian symmetry classification, by developing algorithms to automatically generate all Hamiltonians compatible with given symmetries, or to find all the symmetries of a Hamiltonian. Because topological electronic states reside at the edge of a material, we investigate edges in general terms through a systematic study of boundary conditions for Hamiltonians, by parametrizing the space of physically relevant boundary conditions, and showing how to classify them by symmetry.

We then utilize our general methods in a study of the monolayer molybdenum dichalco- genide family of materials, and discover a previously unknown topological phase. Sec- ondly, we investigate the topological states of superconductors, Majoranas, and propose a new electrical measurement to detect them. Finally, we investigate electron reflection off edges in graphene, and show that the presence of disordered topological edge states leads to a breakdown of the law of reflection.

 

More information?

For access to theses by the PhD students you can have a look in TU Delft Repository, the digital storage of publications of TU Delft. Theses will be available within a few weeks after the actual thesis defence.