The main objective of this project is to develop a multiprobe atomic force microscopy cantilever set-up for mesoscopic transport measurements of two-dimensional materials on length scales as small as a few hundreds of nanometers. The multiprobe cantilever method is very versatile and has a number of important advantages as compared to the conventional Hall-bar method. We will utilize the multiprobe cantilever method to study Bloch oscillations in small-angle twisted bilayer graphene.

Leveraging germanene, a two-dimensional topological insulator, my research aims to enhance the revolutionary potential of materials that conduct electricity without energy loss. This endeavor seeks to tackle the challenge of increasing the number of dissipationless topological states, a critical step toward realizing high-efficiency electronics. By meticulously engineering and scrutinizing germanene nanostructures, I aim to unlock new topological phases and deepen our understanding of quantum interactions. This work promises to advance the scientific frontier of topological materials and lay the groundwork for future technological innovations in low-energy electronics and quantum computing.

We aim to realize dissipationless electronic transport in an electronic kagome lattice, i.e. a two-dimensional (2D) network of corner-sharing triangles, by stacking a twisted germanene layer on-top of another germanene layer. Germanene, the germanium analogue of graphene, shares many properties with graphene. Both 2D materials have a honeycomb structure and host Dirac fermions. There is, however, also a very important difference between these two materials, which plays a crucial role in this proposal. The graphene lattice is fully planar, whereas the germanene lattice is buckled, i.e. the two triangular sub-lattices, labelled A and B, are slightly displaced with respect to each other in a direction normal to the layer. This buckling is a unique feature that offers the possibility to realize an electronic kagome lattice. Owing to this buckling, AA, BB, AB and BA stacked atom configurations occur in four flavors: up-up, down-up, down-up and down-down, respectively. Since these four flavors have different atom-to-atom separations and thus also different interlayer interaction (hopping) energies the moiré lattice is electronically modulated, resulting in an electronic kagome lattice. A twisted bilayer germanene exhibits a moiré pattern consisting of AB and BA stacked domains separated by domain walls. We will apply a transverse electric field in order to break the inversion symmetry of these AB and BA domains. The AB and BA domains have opposite valley Chern numbers and therefore a 2D kagome network of one-dimensional (1D) conducting channels that are protected by no-valley symmetry will emerge at the AB/BA domain boundaries upon the application of an electric field (in 0.6o twisted bilayer graphene we already demonstrated the existence of a 2D triangular network of topologically protected 1D conducting channels). The electronic and transport properties of this 2D kagome network of topologically protected 1D channels will be studied with variable temperature (4-) tip scanning tunnelling microscopy (STM) and spectroscopy (STS). The robustness against backscattering in these 1D channels allows for dissipationless 2D electronic transport in the twisted bilayer germanene and opens the door to novel electronic field-effect based device applications, such as a twisted bilayer germanene transistor.

The global energy consumption for information processing is at an all-time high and still keeps on increasing every year. It is therefore crucial to develop electronic devices that consume less energy. In this project, we will fabricate and scrutinize a novel type of transistor. This transistor will be based on the topological material germanene, a two-dimensional form of germanium. This revolutionary type of transistor operates by using an electric field to turn ON and OFF topologically protected edge channels in germanene, in which current flows without energy loss.

We have studied collective phenomena on metal surfaces with Scanning Tunneling Microscopy and Low Energy Electron Microscopy. We studied the structure and dynamics of self-assembled molecular layers on gold surfaces. Several phases with a hitherto not observed structure are identified and a model for their structure is proposed. We also studied the behavior of a Bi layer on a Nickel surface. We found evidence for a stable wetting layer. The observed diffraction peaks exhibit strong resonant electron scattering into eigen states of the image potential near the vacuum level with periodicity determined by the wetting layer.