HIGH-SPINTERA

Understanding non-equilibrium spin-charge transport mechanisms towards high power and antenna-coupled spintronic terahertz devices

Spintronic THz emitters have become an alternative pulsed photonic source concept as compared to established semiconductor-based devices such as ErAs:In(Al)GaAs, Rh:InGaAs and Fe:InGaAs/InAlAs superlattice structures. Spintronic emitters consist of a few-nm thick stack of ferromagnetic (FM) and nonmagnetic heavy metal (HM) films that can easily be evaporated onto almost any carrier substrate. Like pulsed photoconductors, a <100 fs laser pulse is absorbed by the semi-transparent metal stack. Instead of a DC bias, a DC magnetic field aligns the ferromagnetic material which gives rise to spin-polarization of the photoexcited carriers. The (out of plane) spin current, j_s, is converted into an (in-plane) charge current by the inverse spin hall effect (ISHE). The charge current will then emit THz radiation, either directly (large area emitter concept) or by the aid of an antenna. The figure shows a schematic of a spintronic emitter. It can, in principle, outcompete traditional photoconductive THz emitters in terms of bandwidth, but also possibly in terms of laser-to-THz power conversion efficiency. Furthermore, the layer stacks do not require crystallinity so they can be deposited on any material without the necessity of advanced growth facilities like molecular beam epitaxy.

The goals of this project are:

• Gaining a deeper understanding of the processes happening in spintronic layer stacks
• Improving spintronic emitters both from the material as well as from the electrical engineering point of view
• Applying spintronic materials to use cases with particular focus on areas, where classical photoconductors are difficult to implement or too costly.

The project is a collaboration between the groups of Markus Meinert (TUDa), the group of Dmitry Turchinovich (Univ. Bielefeld) and the TSYS group (Preu). The project is funded through the Deutsche Forschungsgemeinschaft, project number 518575758 (HIGH-SPINTERA)