Electron Transport along Screw Dislocations in a Strong Topological Insulator

In a three-dimensional strong topological insulator, gapless helical surface states appear everywhere on its surface. In the presence of a screw dislocation, gapless helical modes also appear in the vicinity of the corresponding dislocation line. Let us focus on a case where a pair of screw dislocations connects the top and bottom surfaces of a strong topological insulator with a shape of rectangular parallelepiped. The dislocation-induced helical modes are expected to act as one-dimensional conduction channels connecting the top and bottom surfaces. To examine this expectation, we calculate the two-terminal conductance between a pair of electrodes placed on the top and bottom surfaces. We found that the dislocation-induced helical modes and the helical surface states on the side surface contribute to the two-terminal conductance. The contribution of the dislocation-induced helical modes becomes more dominant than that of the helical surface states in certain situations.