TopoGraph · Towards topological hybrid states in graphene
Horizon 2020 — Marie Skłodowska-Curie Actions
- Duration
- 2018-09-01 → 2020-08-31
- EU contribution
- €146,239
- Participants
- 1
- Scheme
- MSCA-IF-EF-ST
Lines connect the coordinator with its partners.
Results in brief
Towards topological hybrid states in graphene
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.
Data: CORDIS, © European Union
Project objective
Majorana fermions (MF) are novel excitations of solid-state nanostructures, which obey non-abelian exchange characteristics. This property, together with their topological protection made MFs candidates for basis of topological quantum computation. So far most of the experimental studies concentrated on 1D nanowire systems. In the project TopGraph we will choose a different path to engineer MFs using 2D systems. Our platform is graphene, a single layer of graphite, which has Dirac spectrum and can be ballistic over tens of micrometers. We will use two systems: 1) twisted bilayer graphene, which is driven into a special quantum Hall state (effectively a quantum spin Hall state) and 2) graphene with SOI induced by other 2D materials., e.g. WSe2 and combed with Zeemann fields. When inducing superconducting correlations to these structures the formation of MFs are expected.First, we will study SC current in these special states, where changes in the SC current and Fraunhofer pattern can reflect transition to topological phases. To prove the existence of the topological excitations, the Andreev bound state spectra of the system will be studied using local tunnel probes, either defined lithographically or using scanning tips. Finally smoking-gun signature of the topological current can be obtained from current phase relation measured using high frequency techniques (with the help of a secondment).The project combines the expertise of the fellow on graphene, with the know-how of the host on hybrid nanodevices and induced superconducting correlations. During the project the fellow will be trained by the host and the secondments in ultra-low-T measurement, scanning probe, dedicated noise filtering techniques, pressure cell studies and fundamentals of topological superconductivity. The proposal opens up new directions in topological computation in 2D materials, and introduces the fellow to this rapidly developing field, which will significantly advance his career.
Original text from CORDIS.
Participants
- BUDAPESTI MUSZAKI ES GAZDASAGTUDOMANYI EGYETEM · BudapestCoordinatorHungary
Links
Data: CORDIS, © European Union