On the trail of novel spintronic and electronic devices via exotic light-matter interactions

Topological states are exotic phases of matter resistant to change. They give rise to phenomena such as crystals that insulate on the inside but conduct electricity on their surfaces (topological insulators) or chiral arrangements of some order parameters in real space. It is also possible to isolate individual topological entities and use them for specific tasks, especially for information technology purposes. The EU-funded TSAR project will investigate topological phenomena in 'unconventional' topological materials where the staggered orders (electric and magnetic) result in a macroscopic cancellation of their built-in fields. This will open new horizons in the manipulation of individual topological solitons at very fast speed.

With the end of Moore’s law in sight, new schemes must be devised to achieve energy efficient, high density and high-speed data storage and processing. One emerging concept in today’s condensed-matter physics that may fuel next-generation information technology is topology. Topological phenomena in real space can give rise to interesting objects (for instance magnetic skyrmions), which are topologically protected, i.e. endowed with an energy barrier associated with a change in their topology class. These solitonic objects have been found mainly in magnetic materials like ferromagnets and there are very recent reports that ferroelectrics may also be able to host them. Interestingly, antiferroic orders like antiferromagnetism or antiferroelectricity would provide extra properties, e.g. a faster motion or an increased robustness. In TSAR, we will design antiferroic systems based on oxide materials where spin and electric dipole textures will be nucleated. We will devise approaches to control these topological solitons using different stimuli, and in particular ultra-fast vortex light pulses carrying angular orbital momentum. Gathering a consortium with broad expertise comprising academic (experimental and theoretical groups) and industrial partners, strategies will be devised and applied starting from high quality materials to devices. The targeted breakthrough of our project is to realize the first proof-of-concept for agile, low-power, room-temperature spintronic and electronic devices based on antiferroic topological materials. Their intrinsic high speed operation and low-power consumption will help tackling present societal challenges. Success in these endeavors will establish topological antiferroic systems as a novel versatile platform for future energy-efficient nanoelectronics.

Domain walls in ferroelectrics are naturally formed 2D solitons with a defined, nm-thick polarization profile stable over macroscopic lateral dimensions. Strong coupling of the polarization gradient with strain drastically changes the material properties within the domain wall thickness. Increasing attention is paid to these mobile interfaces because the characterization tools have recently reached the desired nanoscale resolution, needed to uncover the rich spectrum of new phenomena expected there. We are convinced that some ferroelectrics can also host 1D analogues of domain walls, i.e. spontaneously formed ferroelectric line solitons, similar to the recently experimentally confirmed Bogdanov-Yablonskitype magnetic skyrmion lines. We wish to extend the explorations also to these interesting topological objects and to pave a path to the experimental discovery of the ferroelectric skyrmion phases, analogous to the vortex states in superconductors and skyrmion phases of chiral magnets.

The recently discovered coexistence of both ferroelectricity and non-conventional skyrmionic spin textures in the lacunar spinel GaV₄S₈ (GVS) promises outstanding magnetoelectric effects to happen in these compounds. Notably, GVS is the first and only multiferroic material known to date that potentially might find its way into top-modern applications such as skyrmionic memories. In order to significantly advance the fundamental understanding, we propose in this bilateral project to shed light onto the fundamental static and dynamic behavior of GVS and its related compounds, through the concerted nanoscale approach between theory and experiment. More precisely, we uniquely combine the local-scale experimental inspection (by using various scanning probe techniques and optical spectroscopy) with multi-scale modeling strategies (i.e. ab-initio, phase field modelling, etc.). The two participating teams in Prague/Czech Republic and Dresden/Germany form the ideal basis in order to conduct this research in the proposed bilateral project.

The proposed project will promote a close collaboration between Prague and Dresden teams interested in a same hot research topic of peculiar vortex phases in multiferroic materials. In order to bridge different experimental (Dresden team) and theoretical (mainly Prague team) approaches used in our teams, we plan mutual workshops, training sessions for PhD students and discussion of recent results. We believe that the developed synergy between our teams and a unique combination of the local-scale experimental inspection (by using various scanning probe techniques and optical spectroscopy) with multi-scale modeling strategies (i.e. ab-initio, phase field modelling, etc.) will significantly advance the fundamental understanding to, for example an outstanding magnetoelectric effect in GaV₄S₈, which is the first and only multiferroic material known to date that potentially might find its way into top-modern applications such as skyrmionic memories.