25.02.2020; Vortrag
Ultrafast Spin and Charge Transfer Phenomena in Magnetic and Functional Materials
The growing demand for information technology with higher data processing speed and data storage capacity has started the quest to control and functionalize materials on smaller length and shorter timescales. In this context, optical excitations with femtosecond light pulses offer the intriguing opportunity to control materials on ever-shorter timescales, ultimately down to the duration of the optical excitation itself. In most cases, however, the optically induced dynamics evolve on significantly longer timescales that are dominated by the intrinsic energy, charge and spin transfer processes of the materials. After a detailed introduction into our research, I will focus on two exemplary cases, for which the timescale of the optically induced material response is dominated by spin and charge transfer processes.For magnetic materials, I will introduce a novel approach to control the spin order of magnetic alloys by optically induced spin transfer processes. I will show that fs light pulses with selected photon energies can trigger an ultrafast exchange of spin carriers between the magnetic sub-systems of alloys that can instantly enhance or reduce their spin order [1]. This highly energy efficient process results in a strong non- equilibrium in the combined spin-system of the material that severely affects the subsequent magnetization dynamics medicated by secondary processes such as exchange or spin-flip scattering. Subsequently, I will turn to the optically induced charge carrier dynamics in functional molecular materials. They are particularly interesting due to their complex photo physics that is dominated by bound electron-hole pairs, called excitons. These excitonic quasi-particles can be responsible for a long-lived trapping of charge carriers in these materials. For fullerene complexes, I will demonstrate that the exciton dissociation time of charge transfer excitons [2] in molecular materials can be significantly reduced by additional charge transfer processes due to alkali-metal doping. In this way, my presentation will provide a clear vision for manipulating low dimensional quantum materials, topological systems and spin-ordered functional materials by optically induced and chemically engineered spin and charge transfer processes.
[1] M. Hofherr et al. Sci. Adv. 6 eaay8717 (2020)
[2] B. Stadtmüller et al. Nat. Commun. 10, 1470 (2019)