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Time dynamics and ContROl in naNOStructures for magnetic recording and energy applications

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New tools for studying atomic-level dynamics

EU-funded scientists have developed necessary theoretical tools for addressing ultrafast dynamics of solar energy conversion and laser-induced magnetisation.

Energy

Europe needs to have a variety of sustainable sources of energy, and sunlight is of great interest. The continent also needs vastly improved magnetic storage to cope with the growing flood of data. Although one might not expect a single research project to address both concerns, advancing the theory of ultrafast dynamics in real materials does so. The CRONOS (Time dynamics and control in nanostructures for magnetic recording and energy applications) project successfully developed a quantitative, flexible and fully atomistic theory of ultrafast dynamics. The use of time-dependent density functional theory was a key approach to the investigations. Scientists implemented in both ELK and Octopus mainstream codes a range of tools enabling new calculations, namely periodic boundary conditions for solids and laser pulses of arbitrary intensity and shape. They also invented new exchange and correlation functionals for more accurate calculations of real materials. In groundbreaking work, project members demonstrated energy transfer coherence in organic solar cell materials. In particular, they showed that during exciton formation the charge density and the associated energy oscillate coherently between the donor and the acceptor. Results have far-reaching impact since they validate a large volume of studies on coherent energy transfer in solar energy conversion and potentially in biology. Until now, no dynamics studies on the electronic level have ever been performed on magnetic systems. Scientists sufficiently explained the microscopic processes that drive ultrafast demagnetisation in magnetic metals. A scaling law relating the spin orbit strength and the demagnetisation speed was established and proved. This law applies to all magnetic materials regardless of their macroscopic order (ferromagnetic, antiferromagnetic or ferromagnetic). Furthermore, the team thoroughly investigated the optical responses of interfaces between magnetic and non-magnetic materials. Having advanced the optimal quantum control theory, scientists can now successfully design laser pulses that cause production of high-harmonic generation of molecules. This essentially means it is possible to engineer the frequency response of real objects. Similar work was conducted on the electron spin dynamics of quantum dots and bulk transition metals. CRONOS outcomes have been published in over 140 research articles in peer-reviewed journals. Furthermore, project investigators gave over 100 talks at international events and organised about 20 workshops and symposia at conferences.

Keywords

Ultrafast dynamics, solar energy, magnetisation, magnetic materials, atomistic theory

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