Application of split-gate structures as tunable spin filters

We describe an electron filter that exploits the known magnetotransport pro perties of quantum point contacts to provide local and tunable control of t he spin polarization in a semiconductor. When properly configured, we show that the conductance of this device gives a direct measure of the spin pola rization of carriers transmitted through it. By modeling the transport thro ugh a potential barrier with experimentally realistic parameters, we discus s the factors which must be satisfied in order to successfully implement su ch a device. (C) 2000 American Institute of Physics. [S0003-6951(00)02333-0 ].