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Skyrmion-Topological insulator and Weyl semimetal technology

Periodic Reporting for period 1 - SKYTOP (Skyrmion-Topological insulator and Weyl semimetal technology)

Reporting period: 2018-11-01 to 2020-04-30

SKYTOP-Skyrmion-topological insulator and Weyl semimetal technology
SKYTOP develops a technology based on topological quantum matter that can have an impact on information processing and storage. The project gathers expertise from Greece, France, Germany, Italy and Belgium to face challenges in materials growth, device modelling and evaluation as well as scale-up of the technology for future volume production.

Magnetic materials show unusual swirling configurations of their spin (Skyrmions) characterized by non-trivial topology, while a class of topological materials known as topological insulators (TI) and Weyl semimetals (WSM) show unexpected transport properties due to unusual twisting of their electronic band structure. In SKYTOP we aim to combine these different classes of topological matter and demonstrate that they can lead to new energy efficient ways of manipulating and storing bits of information. It will be a big challenge in this project to show that possible compatibility issues can be overcome and that the new topological materials combinations can be synergetic and fully functional.

The overall objectives of the project are:
• Explore synergies between two classes of topological materials: Skyrmions (topology in real space) and topological Insulators (TI) and Weyl semimetals (topology in reciprocal space). The ultimate goal is to enable low power all-electric skyrmion manipulation for magnetic and spintronic devices.
• Open an exploitation route for Weyls (and TIs) for practical applications. The Spin Hall effect is a key property for Weyls (and TIs) that could lead to important applications if combined with magnetic materials such as Skyrmionic materials. Large area growth by a variety of synthetic thin film growth techniques (MBE, MOCVD, sputtering) as well as a growth scale-up activity are key for the development of manufacturable topological devices in the future.
• Mobilize the emerging community on topological matter. An aggressive outreach activity is envisaged to increase awareness in a wider scientific and technological society about the opportunities offered by topological materials.


Expected impacts on society
Our new skyrmionic magnetic devices, enhanced by TI and WSM materials, offer ultra-low power consumption, and enable the design of next generation neuromorphic devices and circuits with expected impact on artificial intelligence (AI) of the future. AI is expected to penetrate every part of our daily lives at home and work, improving services and security and enhancing the well-being of citizens by enabling for example autonomous driving and health monitoring and prevention.
During the first 18 months, SKYTOP consortium harnessed the necessary synergies among its members and developed suitable protocols for materials properties validation. The effort focused on the development of growth of good quality topological films on large area substrates ensuring that they are suitable for integration with magnetic skyrmionic materials at a later stage. In addition, in this first project period, the consortium set as a target to unveil the interesting properties of topological thin film materials made by synthetic methods on different substrates and verify that they have similar and equally good properties compared to bulk materials grown by equilibrium methods.

The biggest accomplishment in this first period is that the consortium, after screening a large number of topological insulators (TI) and topological Weyl semimetals, selected a number of prospective candidates and is now ready to integrate them with optimum skyrmionic magnetic multilayers to fabricate composite functional devices. Among the TI and Weyl materials selected, there is a number of materials which are grown in new structural phases not studied in detail yet, presenting immense scientific interest. Moreover, other topological materials have been grown directly on technologically important Silicon substrates using synthetic methods fully compatible with industry standards. This creates the prospect that the project results can be exploited by the consortium which gathers the necessary expertise from materials developers to equipment manufacturers and key technology enabling companies/end users
"SKYTOP member CNRS/THALES have demonstrated for the first time at room temperature skyrmions, only 40 nm in size, which ""live"" in a synthetic antiferromagnetic medium. This discovery, published in Nature Materials is very important since it signifies the formation of skyrmions in stray field-free environment, opening the route for the scaling of skyrmions down to the 10 nm scale, which is extremely important for applications.

Max Planck Institute (MPI) have realized new structural phases of Topological Weyl semimetals with Weyl points which are fully accessible to transport exhibiting a strong charge to spin conversion efficiency comparable or better than conventional heavy metal materials. More over, new magnetic Weyl materials produced by Max Planck and characterized by Terahertz spectroscopy reveal an ultrafast spin generation capability comparable to the best known iron-based materials which is considered to be extremely useful for future advanced magnetic information processing and storage devices.

NCSRD and IMEC have explored new structural phases of layered topological insulators not previously studied in detailed and they have verified the presence of topological surface states which is the most important property that makes these materials good candidates for topological insulator/skyrmion composite structures and devices.

While most of the topological insulators are difficult to grow directly on silicon, often requiring expensive substrates or special templates and buffer layers, CNR have managed to overcome this problem and have clearly demonstrated that important topological insulator material can be fabricated with very good quality directly on technologically important silicon substrates using an industry proven methodology. Moreover, the showed that ultrathin magnetic materials can be grown by conformal deposition on the topological insulator which is the first step towards integration of topological insulators with magnetic skyrmion materials to realize functional composite devices.

Several of the aforementioned achievements beyond the state of the art, are enabled by the the active involvement of the equipment manufacturer AIXTRON in our development efforts by providing excellent quality two dimensional layered materials templates for the overgrowth of topological insulators.

The project is expected to make significant contributions in the following years first in the scientific domain with good prospect to discover new phases of topological matter and unveil their exciting new properties, second by scaling up the technology to large area substrates with the aim to commercialize new functional devices made of composite skyrmion topological layers. The envisaged devices are in the area of reconfigurable filters and bio-inspired neuromorphic devices, both relying on the dynamics of skyrmions."
Skyrmions in antiferromagnetic layers (left).Surface states in a topological insulator (right)