Geometrically induced reversion of Hall current in a topological   insulator cavity
  An electric charge near the surface of a topological insulator induces an image magnetic monopole. Here, we show that if the topological insulator surface has a negative curvature, namely in the case of a semispherical cavity, the induced Hall current reverses its rotation as the electric charge crosses the semisphere geometric focus. Such a reversion is shown to be equivalent of inverting the charge of the image magnetic monopole. We also discuss upon the case of a semicylindrical cavity, where Hall current reversion appears to be feasible of probing in realistic experiments. 
Warlley H. Campos, Winder A. Moura-Melo and Jakson M. Fonseca
cond-mat.mes-hall cond-mat.mtrl-sci