PhD: Ultrafast Terahertz Spectroscopy of Multi-Functional Materials

Electromagnetic waves in the frequency range 300 GHz -30 THz have various applications for imaging, chemical detection or high-speed communication. However, convenient emitters and detectors are still missing in this range, known as the THz gap. Existing devices are mostly based on semiconductors and have limited performances. The use of new physical mechanisms, not relying on semiconductors structures, appears as a possible route for the further development of the field of THz physics. In this context, spintronic based technologies appear particularly promising. The discovery of spintronics THz emitters shows that it is possible to outperform laser driven semiconductor THz sources when using a different, spin based, emission scheme. This discovery lead to an unprecedented development of THz spintronics. However, these works are mostly focused on emission and there is a clear need for efficient scheme for THz detection. In this PhD project, we propose to use the antiferromagnetic resonance for spintronic THz detection. The Strasbourg institute of materials physics and chemistry (IPCMS) has over twenty years of expertise in the field of ultrafast magnetism and spintronics within the Department of Ultrafast Optics and Nanophotonics and the Department of Magnetism of Nanostructured Objects. It has several measurement setups dedicated to THz detection and emission. Antiferromagnets have their natural resonance mode in the THz range, due to the strong exchange interaction between their magnetic sub-lattices. In this PhD thesis, we propose to design and use a novel detection scheme consisting in integrating the antiferromagnet within a micrometer scale electromagnetic antenna structure to concentrate the THz field and access antiferromagnetic resonance at a reduced scale. In addition, we will take advantage of the so-called inverse spin Hall effect occurring in a heavy metal layer adjacent to the antiferromagnet to detect the interfacial spin current generated at resonance. The aim of the PhD project is to study experimentally the antiferromagnetic resonance in microstructures. The project includes design and simulation work aiming at optimizing THz confinement. In a second step the most promising devices will be fabricated onto selected antiferromagnetic systems using cleanroom facilities (STnano). The structures will then be characterized using both a time-resolved optical set-up and a continuous wave THz platform (0-1.2 THz). During the thesis, a secondment at SPINTEC (SPINtronique et TEchnologie des Composants) and the LNCMI (national high field laboratory) in Grenoble will aim at adapting the design for measurements at the high magnetic field THz set-up of LNCMI.