Author Description

Topological insulators (TI) are a group of materials that have unique band structures: the surfaces show linearly dispersed bands, while the bulk shows normal conduction bands and valence bands. The carriers located in the surface states are spin-momentum locked, meaning the spin of the surface carriers are dependent on the direction of their motions. Plasmons are the collective oscillations of electrons, affecting the way how electrons in the materials interact with external electro-magnetic waves. Thus, the optical property of a material is largely dependent on the plasmons in it. Due to the spin-momentum locking, the plasmons that are formed by TI surface carriers (known as the Dirac plasmons), are correlated electron density waves as well as spin density waves. These spin density waves are essentially spin plasmons. The direct experimental evidences of this prediction remain unveiled. Therefore, the ultimate goal of this dissertation is to experimentally reveal the charge density oscillations and spin density oscillations at the mean time.