Graphene, a single sheet of graphite, is one of the most promising materials of nanoelectronics: it has, among other properties, ultra-high mobility, which combined with the linear electron spectrum makes table top relativistic experiments possible. Graphene can also be combined with other 2D materials for electron-optical experiments, for spintronics and for realizing new, topological phases. The most widely used method for realizing high mobility graphene is to encapsulate it between hexagonal boron nitride (hBN) crystals. In recent years, it has been realized, that further developing this method novel materials can be engineered. The LEGO-style building is called van-der Waals stacking, and several building blocks of other 2D materials have been identified. Among these semiconductor, superconducting, magnetic and materials with larger spin-orbit interaction have been identified, that can be used to introduce superconducting or spin correlations into graphene.
The goal of the PhD work is to realize and study topological phases by combining novel 2D materials. Several experiments have suggested that a quantum spin Hall phase can be realized in graphene. Coupling this phase to superconducting electrodes topological excitations, Majorana and parafermions can be realized. These excitations form the basis of topological quantum computation and have non-Abelian exchange statistic. Further it will be interesting to study the supercurrent appearing in the quantum Hall phase. Several interesting proposals have appeared for the applications of these nano-circuits, like a Cooper pair splitting circuit, which can be used as a source of entangled electrons.
|Left: Graphene based superconducting interference device (SQUID). Right: False colored electron beam image of a graphene based heterostructure (Source: P. Makk, C. Handschin).|
During the PhD work the candidate will be involved in engineering novel 2D heterostructures, where graphene will be combined with other materials (like strong spin-orbit TMDCs) and with superconducting contacts to realize new state of matters. The candidate will use electron-beam lithography to realize the nano-circuits (Hall bars, Josephson junctions etc.) and will study these circuits at ultra-low temperatures. The work is done in close collaboration with several European universities.
Knowledge of solid state physics, motivation for experimental work, English knowledge, basic programming and measurement automation experience.