Public defence in Engineering Physics, M.Sc. Guangze Chen

Title of the doctoral thesis: Designing exotic phases of matter with magnetic van der Waals materials

Doctoral student: Guangze Chen
Opponent: Professor Nuno M. R. Peres, University of Minho, Portugal
Custos: Assistant Professor Jose L. Lado, Aalto University School of Science, Department of Applied Physics

Exploring rare and fascinating forms of matter is of crucial fundamental and applicational interest. An essential ingredient in a variety of exotic phases including quantum spin liquids, topological superconductivity, and heavy fermions is quantum magnetism. Despite the excitement surrounding these unusual phenomena, remarkable challenges remain in identifying and studying them in real-world materials. Fortunately, recent advancements in magnetic van der Waals materials, some of which provide a realization of quantum magnetism in the realm of two dimensions, provide a promising avenue for tackling these challenges. Due to their two-dimensional nature, they provide a versatile platform for designing exotic phases of matter. In this thesis, we explore via theoretical techniques how exotic phases of matter can be realized and identified with magnetic van der Waals materials. In particular, we present three approaches. 

In the first approach, we show that manipulating the magnetic van der Waals material with an impurity, a twist, or a substrate allows to realize and probe Dirac quantum spin liquids. In the second approach, we show that a magnet/metal heterostructure can be utilized to design helical states or heavy fermions, with the latter being experimentally realized in the 1T/1H-TaS2 heterostructure in the Atomic Scale Physics group at Aalto University. In the third approach, we investigate how the Coupling between the quantum magnet and its environment, which usually causes unwanted effects, can actually be beneficial in creating robust and protected excitations. 

Throughout the above studies, we have implemented a variety of state-of-the-art numerical tools. In particular, we developed two computational libraries "Twistronics.jl" and "NHKPM.jl" for people to reproduce our results or to conduct their own research. Our research highlights the versatility of magnetic van der Waals materials for engineering novel phases of matter. It also provides valuable insights for experimental research in this field. By expanding our understanding of these materials, we can pave the way for further investigations into other fascinating phases, such as multiferroics. Beyond our scientific findings, our computational libraries provide a starting point in theoretical studies on these systems.

Thesis available for public display 10 days prior to the defence at: 
https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

Contact information:

Doctoral theses in the School of Science: https://aaltodoc.aalto.fi/handle/123456789/52