Ultrafast Coherent Optoelectronics & Magnetism
We develop novel experimental tools to investigate electronic and magnetization dynamics with attosecond temporal resolution.
Magnetism:
Though technologically extremely appealing, the manipulation of spins with ultrafast light waveforms is impeded by the weak coupling between light and spin degrees of freedom. Rather, spin-orbit coupling governs the spin dynamics after optical excitation due to the strong electric fields close to the nuclei of a material. With spin-orbit-coupling times in a solid on the order of 10s of femtoseconds or longer these dynamics decouple significantly from the sub-femtosecond response of the electronic configuration to an excitation field.
Yet, recent theoretical studies indicate a possibility of sub-femtosecond magnetization control in multi-sub-lattice materials. The key to this ultrafast spin dynamics are inter-sub-lattice charge excitations, which are also associated with inter-site spin transfer. This concomitant spin-current then triggers a macroscopic change in magnetization and paves the way to light frequency magnetization control.
We set up an experimental program dedicated to the exploration of this ultrafast, coherent light-field controlled magnetics scrutinizing attosecond magnetization dynamics in alloys and magnetic multi-layer structures.
The project seeks to increase our understanding of the fundamental concepts of modern magnetism, with particular emphasis on the timescale of the initially coherent and non-dissipative light-matter interaction. We seek to provide information about the magnetic coupling within few-atom thickness magnetic multilayer structures as well as in multi-constituent magnetic alloys. The anticipated outcome will be relevant for the development of novel approaches for ultrafast and nm-confined magnetic recording and spintronics/spin-photonics.
Optoelectronics:
The origin of the functionality of electronic devices is in electron dynamics inside the complex energy band structure of condensed phase systems. After an external field promoted electrons into conducting states, several highly dynamical pathways conspire to randomize energy and momentum of the excited electrons. These interactions, foremost electron-electron and electron lattice scattering lead to the thermalization of the carriers to the band extrema or, equivalently, the minimization of the electron-hole binding energy on characteristic timescales of tens of femtoseconds (electron-electron) to picoseconds (electron-lattice).
If coherent light fields are used to excite, the situation can be dramatically different. Outpacing thermalization with few-femtosecond laser pulses results in the laser field imprinting its coherence properties onto the initial excitation distribution. Our recent studies focused on this aspect are enabling to explore light-matter interaction taking place within a fraction of an oscillation cycle of a visible light field and we envisage that this opens the domain of petahertz electronics. With novel experimental tools we seek to explore light-field controlled electronics and the coherent nature of electronic motion on the femtosecond-to-attosecond time scale.