  In this paper we study a non-equilibrium resonant tunnelling problem where a
non-interacting quantum dot is connected to two leads, one being the edge of an
interacting 2-D topological insulator (Luttinger liquid) and the other being a
usual Fermi liquid. We show that the current passing through the system can be
expressed in terms of a non-equilibrium local single-particle Green's function
of the Luttinger liquid lead which can be analysed using standard bosonization-
Renormalization Group (RG) technique. In particular, some exact results can be
extracted in the small bias limit with repulsive electron-electron interaction.
A simple formula which captures the qualitative feature of the I-V relation
over whole temperature and voltage bias range is being proposed and studied.
