Magneto-optical effects in hybrid plasmonic nanostructures

Abstract

This thesis focuses on magneto-optical effects and their enhancement at optical resonances in hybrid plasmonic nanostructures. One of the main goals is to gain a better understanding of the transverse magnetic routing of light emission (TMRLE) regarding both components of the hybrid plasmonic-semiconductor model system used to investigate this novel effect. Here, the TMRLE describes the routing of light emitted from excitons in a diluted magnetic semiconductor (DMS) quantum well (QW), where the selection rules of the exciton optical transitions are modified by an external magnetic field to have a non-zero transverse spin along the magnetic field direction. By placing the light source near a surface, it can couple to subwavelength evanescent optical fields, such as surface plasmon polaritons (SPPs), which possess a strong transverse spin and spin-momentum locking. This translates the spin of the emitter into a routed wave along the surface and directional emission into the far-field. Firstly, the temperature dependence of the routing from the DMS QW, used as strongly polarizable light source, is investigated. The findings reveal a significant decline in the achievable emission routing for increasing temperatures, but also the emergence of the light-hole emission, which is routed in the opposite direction to the main heavy-hole emission. Additionally, alternative non-DMS-based QW structures are explored as potential candidates for achieving temperature-independent emission routing. Secondly, the influence of the plasmonic nanograting, the other constituent of the hybrid structure, on the enhanced routing is demonstrated. The emission directionality is investigated for various grating periods and slit widths, which also reveals the usually hard-to-detect weak coupling between the QW excitons and the SPPs as a large contributor to the emission directionality spectrum. Lastly, the thesis explores the transverse magneto-optical Kerr effect (TMOKE) for light reflected from or transmitted through a magnetite-based plasmonic waveguide structure. Here, the hybridization of the plasmonic and magnetic waveguide modes leads to a wide-band enhancement of the TMOKE signal in transmission.