Department or Program


Primary Wellesley Thesis Advisor

Robbie Berg

Additional Advisor(s)

Nuh Gedik, MIT


A topological insulator (TI) is a type of quantum material that is insulating in the bulk but metallic on the surface. Due to the unique spin properties of the surface electrons, TIs have attracted much interest for their potential applications in spin-based electronics and quantum computers. Even more exotic effects occur when TIs are brought in contact with magnetic materials. This thesis represents a study of two-layer thin films consisting of the TI Bi2Se3 and the magnetic insulator EuS using a nonlinear optical technique called second harmonic generation (SHG) imaging. SHG imaging can probe the crystal and magnetic structure at the surfaces and interfaces of inversion symmetric materials. At the interface between the EuS and Bi2Se3 layers, magnetic domains are expected to form. The domain boundaries are predicted to host chiral edge states, which are dissipationless currents that flow in one direction around a domain. Using SHG imaging, our goal was to visualize the magnetic domains in this magnetic topological insulator system. Even though we have yet to observe any evidence of magnetic domains in this material, we also performed SHG imaging on monolayer MoS2 and were able to visualize distinct crystal grains. Our SHG imaging setup that was improved upon during this thesis has the potential to reveal information about other interesting quantum materials.