Colloquia

This year marks two decades since the theoretical discovery of the quantum spin Hall effect. It is exhibited in two-dimensional insulators with a topologically non-trivial band structure, which leads to the existence of helical edge states. The theoretical proposals were soon followed by an experimental discovery of the quantum spin Hall effect in HgTe/CdTe heterostructures. Since then, thousands of papers have been written on the subject, yet very few (perhaps only two) relevant materials have been discovered, and very few theoretical works have claimed to quantitatively explain experimental data. One such material, now established to exhibit the quantum spin Hall effect, is the monolayer tungsten ditelluride. In addition to the quantum spin Hall state, it hosts a correlated insulator ground state at low doping, as well as superconductivity at high enough electronic density. This material will be the main focus of the talk.

After a brief of the research pursued in my group, I will describe our efforts to explain experimentally observed singular linear and nonlinear magnetotransport on the helical edge of the monolayer tungsten ditelluride. I will discuss a model of bulk midgap states "side-coupled" to the edge which appears to account for many experimental features, particularly the dependence of various transport coefficients on the direction of the external magnetic field, as well as their singular dependence on its magnitude.