Spectroscopy and imaging of spin waves and valley excitons in two dimensions

Knowledge about the magnetic and electronic properties of materials does not only expand our fundamental understanding of nature, but is also crucial for the development of new technologies. Today’s electronic devices rely on electrical currents to transport and process information, which generate a lot of heat waste via Joule heating. These devices could become much more energy efficient by using the electron’s spin or valley degree of freedom to encode information, rather than its charge. In this dissertation we study the elementary excitations of magnetic and semiconducting materials, called spin waves and excitons, which have been proposed as respectively spin and valley information carriers in future electronic devices...