In solid-state physics, theoretical models form the basis for understanding the world. This thesis develops such a mathematical model for plasmons: collective, wave-like vibrations in the “sea of electrons” of a conductive material. Just like waves on the surface of the ocean, these plasmons move across a two-dimensional plane. The major advantage of plasmons is their very small wavelength, much smaller than that of light with the same frequency, which enables the miniaturisation of optical chips.
To predict the behaviour of plasmons in realistic, non-uniform materials, we use semiclassical theory (semiclassical approximation). This allows us to describe how these “electron waves” respond to disturbances. We discuss three applications:
- Scattering: How plasmons deflect and interfere when they encounter an “island” with, for example, a different electron density.
- Waveguides: How we can “capture” and steer plasmons in specially designed channels.
- Periodic structures: How a series of these channels forms a “band structure”, which functions as a filter to allow only plasmons with specific energies to pass through.
This research provides a fundamental guide for steering waves in the electron sea, a crucial step towards future plasmonic technologies.
Tjacco Koskamp (born in 1995 in Beugen) studied Applied Physics at Eindhoven University of Technology, where he obtained his bachelor's degree in 2018. For his bachelor's project, he investigated the spin Cherenkov effect in the Physics of Nanostructures group. He continued his studies with a Master's degree in Applied Physics. During an internship at Tohoku University in Japan, he worked on the dynamics of skyrmions. His graduation project, on spin-vorticity coupling, deepened his interest in theoretical physics. He graduated in 2020. In 2021, he started his PhD at Radboud University in Nijmegen, researching “plasmonics”. He worked on the semi-classical description of plasmons in inhomogeneous 2D media. In addition to his research, he was involved as a teaching assistant and as a board member of the PhD Panel.