Application of split-gate structures as tunable spin filters

We describe an electron filter that exploits the known magnetotransport properties of quantum point contacts to provide local and tunable control of the spin polarization in a semiconductor. When properly configured, we show that the conductance of this device gives a direct measure of the spin polarization of carriers transmitted through it. By modeling the transport through a potential barrier with experimentally realistic parameters, we discuss the factors which must be satisfied in order to successfully implement such a device.