We study the transport properties of a four-terminal corner junction made by
etching a two- dimensional topological insulator to form a quantum point
contact (QPC). The QPC geometry enables inter-boundary tunneling processes
allowing for the coupling among states with different helicity, while the tight
confinement in the QPC region activates charging effects leading to the Coulomb
blockade physics. Peculiar signatures of these effects are theoretically
investigated using a scattering field theory modified to take into account the
electron-electron interaction within a self- consistent mean-field approach.
The current-voltage characteristics and the current fluctuations (noise) are
derived beyond the linear response regime. Universal aspects of the thermal
noise of the corner junction made of helical matter are also discussed.Comment: 13 pages, 8 figure
