Quantum interference and entanglement of helical supercurrents in Dirac materials

• Applicant: Dr. Grigory Tkachov, Ph.D.
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 292118933

There is currently much effort being put into understanding superconducting phenomena in materials with nodal Dirac-like fermions such as graphene, topological insulators, silicene, molybdenum disulfide, just to name a few. In these materials, electronic processes are influenced by geometric (Berry) phases caused by the coupling of the carrier spin (or pseudospin) and momentum directions, also referred to as helicity. It is responsible for rather peculiar properties of Dirac materials, from the suppression of elastic backscattering and weak antilocalization to the predicted p-wave superconductivity and topological degeneracies associated with Majorana zero modes. While the latter topic has already received considerable attention, many related issues of superconducting Dirac systems still remain barely explored. This project addresses one of such issues, namely the detection and quantum control of helical supercurrents in Dirac materials. An important step in that direction has been done in recent experiments on two-dimensional topological insulators implemented as Josephson weak links between two superconductors. Such hybrid structures act as nanoscale superconducting quantum interference devices (nano-SQUIDs) in which the interference occurs between helical edge currents and is controlled with high precision by an external magnetic flux. These findings may pave the way towards potential applications in magnetometry of ultra-small objects and in engineering of new qubit systems using entangled helical currents. Apart from possible applications, superconducting quantum interference may provide a tool for detecting topological zero modes in transport measurements. The project aims to assess these prospects theoretically by developing a microscopic description of quantum interference and entanglement for helical supercurrents in different nano-SQUID structures.

• DFG Programme: Research Grants