  The possibility of electron beam guiding is theoretically explored on the
surface of a topological insulator through the proximity interaction with a
magnetic material. The electronic band modification induced by the exchange
coupling at the interface defines the path of electron propagation in analogy
to the optical fiber for photons. Numerical simulations indicate the guiding
efficiency much higher than that in the "waveguide" formed by an electrostatic
potential barrier such as p-n junctions. Further, the results illustrate
effective flux control and beam steering that can be realized by altering the
magnetization/spin texture of the adjacent magnetic materials. Specifically,
the feasibility to switch on/off and make a large-angle turn is demonstrated
under realistic conditions. Potential implementation to logic and interconnect
applications is also examined in connection with electrically controlled
magnetization switching.
