Kondo tunneling into a quantum spin Hall insulator

The physics of a junction composed of a normal metal, quantum dot, and two-dimensional (2D) topological insulator (in a quantum spin Hall state) is elucidated. It manifests a subtle combination of Kondo correlations and quantum spin Hall edge states moving on the opposite sides of the 2D topological insulator. In a narrow strip geometry these edge states interact and a gap opens in the edge state spectrum. Consequently, Kondo screening is less effective and that affects electron transport through the junction. Specifically, when edge state coupling is strong enough, the tunneling differential conductance develops a dip at zero temperature instead of the standard zero-bias Kondo peak.