Hello, So a topological insulator can induce a magnetic field when an electric charge is near to it (I can give a reference if necessary), but the thing is, the paper interprets the origin of this magnetic field as being the hall currents on the surface of the topological insulator. Now I don't see the connection between hall currents and topological insulators? Is it obvious that there should be a thing as a hall current on the surface? Or is it only understandable through teneous quantum mechanical calculations relying on spin-orbit coupling? Note that I know a little about what quantum hall effect and quantum spin hall effect have to do with topological insulators (the latter being a topological insulator), but in each of these cases, it didn't come across to me that the hall current was playing a role in the story. So maybe I'm overlooking something at that basic level. The easiest "solution" would be "the edge current on the boundar of a quantum hall effect state and e.g. vacuum is a hall current", but I don't think that is true.