Topologically Protected Boundary Modes in 2D and 3D materials

Topological insulators and superconductors host exotic boundary states with unique properties such as Dirac dispersion and chiral spin texture. The helical and chiral edge modes of a two-dimensional TI can carry dissipationless currents while similar modes in topological superconductors are expected to be (the elusive) Majorana fermions which are thought to be useful for quantum computation. Realizing and measuring the properties of these modes is therefore fundamentally and technologically interesting. In this talk I will introduce the essential concepts of topologically non-trivial materials and present scanning tunneling microscopy (STM) studies of a few different types of topological materials: a two-dimensional topological insulator (monolayer film of 1T-WTe2) and a three-dimensional superconductor (FeSeTe). I will show STM images of topological boundary modes in both systems and show evidence for existence of Majorana fermions in FeSeTe. As time permits, I will show how STM can be used to image the wavefunctions of chiral edge modes in Co3Sn2S2.

Speaker: Vidya Madhavan, University of Illinois, Urbana-Champagne