Non-magnetic defects in the bulk of two-dimensional topological   insulators
  We found that non-magnetic defects in two-dimensional topological insulators induce bound states of two kinds for each spin orientation: electron- and hole-like states. Depending on the sign of the defect potential these states can be also of two kinds with different distribution of the electron density. The density has a maximum or minimum in the center. A surprising effect caused by the topological order is a singular dependence of the bound-state energy on the defect potential. 
Vladimir A. Sablikov and Aleksei A. Sukhanov
cond-mat.mes-hall