Public defence in Engineering Physics, M.Sc. Viliam Vaňo

Title of the doctoral thesis: Designing quantum matter in two dimensions

Doctoral student: Viliam Vaňo
Opponent: Prof. Ronny Thomale, Julius Maximilian University of Würzburg, Germany
Custos: Prof. Peter Liljeroth, Aalto University School of Science, Department of Applied Physics

Exotic states of matter are of fundamental interest in condensed matter physics and attractive due to their possible applications in quantum technology. Recently, a novel designer approach has emerged as a powerful way to engineer these states in artificially created structures, overcoming the limitations imposed by the traditionally studied compounds. This approach provides a highly tuneable platform for realizing and studying various phases of matter. We employ this approach by creating two-dimensional van der Waals (vdW) systems using molecular beam epitaxy and probe them using scanning tunneling microscope (STM). 

In this thesis, we realize three vdW systems hosting heavy fermions, topological superconductivity and unconventional superconductivity. Heavy fermions are realized by creating a vertical heterostructure of a monolayer magnetic and metallic materials, leading to Kondo lattice physics. Using STM, we probe the heterostructure in two setups and show the emergence of Kondo lattice on the magnet side and heavy fermion hybridization gap on the metal side. In the second work, we realize topological superconductivity by creating a vertical heterostructure of a vdW magnet and a vdW superconductor, where the appearance of the Yu-Shiba-Rusinov bands and edge states suggest the topological nature of the heterostructure. Furthermore, in a follow-up work we show the topology of the system is enabled by the moiré effect between the two layers. In the last work, we create a monolayer vdW material and show evidence that it hosts unconventional superconductivity: V-shaped superconducting gap, many-body excitations and pseudogap. 

These results demonstrate the benefits of the designer approach and open new opportunities in condensed matter physics and realizing designer electronic states in vdW heterostructures.

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