  Magnetic texturing on the surface of a topological insulator allows the
design of wave guide networks and beam splitters for domain-wall Dirac
fermions. Guided by simple analytic arguments we model a Dirac fermion
interferometer consisting of two parallel pathways, whereby a newly developed
staggered-grid leap-frog discretization scheme in 2+1 dimensions with absorbing
boundary conditions is employed. The net transmission can be tuned between
constructive to destructive interference, either by variation of the
magnetization (path length) or an applied bias (wave length). Based on this
principle, a Dirac fermion transistor is proposed. Extensions to more general
networks are discussed.
