  We consider a quantum spin Hall system in a two-terminal setup, with an
extended tunneling contact connecting upper and lower edges. We analyze the
effects of this geometry on the backscattering current as a function of
voltage, temperature, and strength of the electron interactions. We find that
this configuration may be useful to confirm the helical nature of the edge
states and to extract their propagation velocity. By comparing with the usual
quantum point contact geometry, we observe that the power-law behaviors
predicted for the backscattering current and the linear conductance are
recovered for low enough energies, while different power-laws also emerge at
higher energies.
