  A quadruple quantum-dot (QQD) cell is proposed as a spin filter. The
transport properties of the QQD cell were studied in linear response regime on
the basis of the equations of motion for retarded Green's functions. The
developed approach allowed us to take into account the influence of both intra-
and interdot Coulomb interactions on carriers' spin polarization. It was shown
that the presence of the insulating bands in the conductance due to the Coulomb
correlations results in the emergence of spin-polarized windows (SPWs) in
magnetic field leading to the high spin polarization. We demonstrated the SPWs
can be effectively manipulated by gate fields and considering the hopping
between central dots in both isotropic and anisotropic regimes.
