Spintronic THz Emission Nanoscopy

Prof. Xiaojun Wu
Beihang University, Beijing, China


As one of the best candidates for the next-generation novel THz sources, spintronic THz emitters (STEs) feature numerous merits including high efficiency, high beam quality, highly stable, ultrabroadband, easy-to-integration and so on. Rapid progresses have been achieved these years based on STEs, such as the generation of >1.5-MV/cm strong-field THz pulses, demonstrating the radiation of continuous THz waves based on DFB-lasers, and realizing external magnetic field free STEs based on antiferromagnetic materials and ferromagnetic metal heterostructures. However, the spatiotemporal imaging of the ultrafast femtosecond spin currents down to nanoscale have not yet investigated. Here we systematically demonstrate the generation and detection of the high signal-to-noise spintronic THz emission from W|CoFeB|Pt heterostructures with the spatial resolution down to ~50 nm by employing an ultrafast THz scattering-type scanning near-field microscope (THz s-SNOM). Thanks to the local confinement and field enhancement, detectable THz radiation was observed under the excitation of 0.5-mW from a fiber laser oscillator. With this method, the efficient injection and precise coherent detection of ultrafast THz spin currents at the nanoscale can be achieved. Furthermore, spintronic THz emission nanoscopy is an effective method that does not require invasion for characterising and etching nanoscale spintronic heterostructures. The cohesive integration of nanophotonics, nanospintronics, and THz-nano technology into a single platform is poised to characterize the spin state at the micro-to-nanoscale density, accelerate the development of high-frequency spintronic optoelectronic nanodevices and other revolutionary technical applications.