Markus Münzenberg
THz spintronic emitter have been proven to be a powerful method to look into spin currents on ultrafast time scales, on subnanometer length scales in metals, topological insulators, at spintronic interfaces and even oxides. For local spectroscopy of ultrafast transport processes however this method just reveals its high potential. In my tutorial I will discuss the possibilities of the THz signal to explore microscopic processes in spintronic devices, the possibility to use THz spintronics to induce picosecond current pulses and to use THz spintronic emitters for superresolution scanning spectroscopy.
Already in the first publication of spintronics THz emitters in 2013, the original sheet current was calculated, which hat an impressive rising edge within 100fs. However, it took many years until the direct measurement of the charge current pulse was realized with a 50 GHz bandwidth using high frequency probes, demonstrating that THz spintronic emitters can also be used for increasing the bandwith of ultrafast electronics. Another way to demonstrate their capabilities for 6G is to couple them directly into split ring resonator in the near field. A spatial mapping of the coupling strength between a local terahertz source on a spintronic emitter and far-field light mediated can be demonstrated by extracting the THz mode structure. This offers the possibility of THz resonator metasurfaces.
In a much simpler way, THz spintronics emitters in the near field can be used for a spatial resolved THz spectromicroscopy. To overcome the optical resolution, connected to the submillimeter wavelength, we go beyond Abbes law of diffraction. This enables us to develop a ultrahigh superresolution method based on a femtosecond laser scanning technique approaching micron resolution for submillimeter THz wave lengths. It can be employed to study magnetic objects and micron sized spin structures, spectroscopic fingerprints of polymers, and even living cells via this scanning technique. Because of its intrinsic spectroscopy information in each point, is has the potential to study transport and spin wave dynamics locally.
At the end, spintronic THz emitters have also a great value for the optimization of spin-orbit torque oscillators. The THz emission probes the conversion efficiency of spin-currents and spin current injection. Vice versa the strength of spin-orbit torque at interfaces is related to the same effects. By combining both, we use this information to optimize spin-torque-nano oscillators (STNOs) for neuromorphic computing chips within the SpinAge project that aims to develop neuromorphic complex feedback structures based on light-control of combined memristive magnetic nanooscillators.
We acknowledge funding by ERC-FET H2020-FETOPEN Proposal “SpinAge” and BMBF META-ZIK project “PlasMark” Unternehmen Region.