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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - HiTIMe (High Frequency Topological Insulator devices for Metrology)

Teaser

Summary

In this project we study and exploit the properties of 3D topological insulator (TI) materials incorporated into high frequency devices. The main driver of the project is the prospect of using a TI nanoribbon to create a topologically protected single-electron charge pump that can be used as a metrological quantum current standard, or in other words to lay the technological foundations for a TI-based device that can realize the SI Ampere.

An accurate charge pump that can operate at temperatures and magnetic fields achievable using affordable table-top systems would be of immediate use in the realization of the Ampere. The technological development in this project will lay the groundwork for charge pumping in TI nanoribbons, as well as for other devices that exploit the unique properties of TI for high-frequency applications including sensing, precision measurement and topologically protected quantum computation.

Materials science has always been intertwined with the development of new electronic devices and new innovations are rapidly adopted by industry and the research community if it is shown that they enable novel functionality or economic benefits. Topological insulators is an example of a new class of quantum materials that is on the cusp of finding applications in electronic devices. Focus so far has mostly been on improving our understanding of the many fascinating properties of TI materials, but it is now becoming clear that they possess electronic properties that make them interesting for a wide range of applications.

Work performed

The initial work has been focused on setting up all the required infrastructure to carry out the research within the consortium, implement the project management structure and create a framework for public outreach.

WP1 has seen the development of novel high quality materials: work on both charge doping, for suppression of TINR bulk conductance (giving access to the TI surface states alone), and magnetic doping to control the TI surface state gap has begun with promising initial results. These new materials result in high quality stoichiometric TINRs with modified properties.

In WP2 we have started to develop the necessary measurement tools to rapidly characterise a large number of TINRs; crucial for optimization of growth and device development. This includes various scanning probe techniques such as sSNOM and scanning microwave probing to wirelessly access the TINR properties. We have also set up initial experiments for cryogenic 4-probe measurements, including microwave characterisation, and have started to gain a deeper understanding of the local THz response of TINRs.

In WP3 we have demonstrated gating of a single TINR through the Dirac point on STO substrates, a major achievement. This is a crucial step towards the required control of TINR properties for implementing useful devices not influenced by the bulk. Tunable resonators for wireless interrogation of TINRs have also been developed and theoretical analysis shows that this could potentially be a direct route towards demonstrating the presence of the TI surface state in devices.

Preliminary results from theoretical modelling throughout the various WPs have been used to explore and evaluate the feasibility of various device implementations towards our vision, a process done in close collaboration with experimental activities to make sure we end up with realistic proposals for device designs.

In summary, during the first year of the project we have laid a good foundation for the full toolbox required to develop practical, controllable, devices from TINR, by combining novel approaches in synthesis, materials characterisation and device fabrication.

Final results

Progress beyond state of the art: So far, the major leap forward is a new understanding of the impact the substrate has on the doping/charge accumulation of the TI surfaces. One potential solution has also been found where we are now able to gate the TI surfaces through the Dirac points, demonstrating detailed control of the TINR conditions. Several other tasks in the project have also lead to new results which will be summarised in 7 papers currently in preparation or under review. Further scientific impact has been delivered through 10 conference presentations throughout the reporting period.

We expect these initial results to provide a solid foundation to the next phase of the project where specific devices will be developed to investigate single charge dynamics in the high quality TINR materials. Together with theoretical modelling and new device concepts we expect to develop new types of TI-based electronic devices which may find many future uses in nanotechnology applications.

Socio-economic impact: The project has now employed 6 new personnel out of which 4 are full time PhD students. Training and working in the leading scientific environments provided by the partner organisations will lead to highly skilled personnel and future European scientific leadership.