In recent years low dimensional materials got to the forefront of research for future electronic devices. These materials promise also new functionalities: examples are topological computation or electron-optics. Although many other layered materials have been discovered, graphene, a single layer of graphite, is the promising among them. Graphene is the wonder material: it has exceptional mechanical and optical properties, has high mobility and a Dirac electronics spectrum which enables the realization of “table-top high energy” experiments.
Topological insulators (TI) are novel state of matter, where symmetry protected edge modes form. Unfortunately, high quality topological insulators are still missing, due to high bulk conductivity or to the low mobility of these materials, but using graphene as a platform some of these problems can be circumvented. The combination of topological insulators with superconducting (SC) contacts can lead to the formation of novel excitations, non-abelian Majorana fermions (MFs) and parafermions (PFs). While there is extensive research both in the field of graphene and in the field of topological materials, graphene as a platform for topological superconductivity has not yet been demonstrated experimentally.
The objective of the project was to harness the exceptional electronic properties of graphene based van der Waals heterostructures, and engineer topological phases and excitations of graphene. To do so, graphene heterostructures with induced spin-orbit interaction and special quantum Hall states of twisted bilayer graphene (TBLG) have to be combined with SC contacts. On the crossroad of these different states of matter topological excitations are formed. The proposal lied on the border or several research fields: 2D materials, quantum computation, superconductivity and spintronics.
The conclusions from the project were the following: High quality Josepshon junctions have been fabricated and studied from graphene with proximity spin orbit coupling (SOC) induced by a WSe2 substrate and from TBLG (for the first time). We have measured the CPR in the double layer system (at a secondment in the nanoelectronics group in Basel), and started the measurements on the SOC system. We have demonstrated the topological nature of the double layer system via Quantum Hall measurements. We have also developed tunnel probes on graphene which we used to study the non-equilibrium distribution function in graphene. Moreover, straining and pressurizing stacks have been shown as novel and promising methods towards manipulating high quality van der Waals heterostructures.
