  We study spin-dependent transport through a quantum nanostructure composed of
a quantum dot (QD) surrounded by a quantum nanoring. The nanostructure is
side-attached to source and drain electrodes and we assume that the confining
potential that forms the nanostructure can be controlled by electrical gating.
We demonstrate that depending on the model parameters the system can exhibit
positive as well as negative differential conductance (NDC). What is more
interesting, these properties can be easily controlled by tuning the applied
gate voltage.
