  We investigate the electrical switching of charge and spin transport in a
topological insulator nanoconstriction in a four terminal device. The switch of
the edge channels is caused by the coupling between edge states which overlap
in the constriction and by the tunneling effects at the contacts and therefore
can be manipulated by tuning the applied voltages on the split-gate or by
geometrical etching. The switching mechanism can be conveniently studied by
electron interferometry involving the measurements of the current in different
configurations of the side gates, while the applied bias from the external
leads can be tuned to obtain pure charge or pure spin currents (charge- and
spin- bias configurations). Relevant signatures of quantum confinement effects,
quantum size effects and energy gap are evident in the Fabry-Perot physics of
the device allowing for a full characterization of the charge and spin
currents. The proposed electrical switching behavior offers an efficient tool
to manipulate topological edge state transport in a controllable way.
