  We investigate electron transport through an antidot embedded in a narrow
strip of two-dimensional topological insulator. We focus on the most generic
and experimentally relevant case with broken axial spin symmetry.
Spin-non-conservation allows additional scattering processes which change the
transport properties profoundly. We start from an analytical model for
noninteracting transport, which we also compare with a numerical tight-binding
simulation. We then extend this model by including Coulomb repulsion on the
antidot, and we study the transport in the Coulomb-blockade limit. We
investigate sequential tunneling and cotunneling regimes, and we find that the
current-voltage characteristic allows a spectroscopic measurement of the
edge-state spin textures.
