  Quantum spin Hall insulators, recently realized in HgTe/(Hg,Cd)Te quantum
wells, support topologically protected, linearly dispersing edge states with
spin-momentum locking. A local magnetic exchange field can open a gap for the
edge states. A quantum-dot structure consisting of two such magnetic tunneling
barriers is proposed and the charge transport through this device is analyzed.
The effects of a finite bias voltage beyond linear response, of a gate voltage,
and of the charging energy in the quantum dot are studied within a combination
of Green-function and master-equation approaches. Among other results, a
partial recurrence of non-interacting behavior is found for strong
interactions, and the possibility of controlling the edge magnetization by a
locally applied gate voltage is proposed.
