Magnetically tunable spin filtering in semiconductor nanowires.

We investigate resonant transmission and spin filtering in symmetric semiconductor nanowires (SSNs), where Rashba spin-orbit coupling (SOC) is symmetrically distributed by applying external electric field. It is shown that electronic bandgap structure has been formed, and the width of the bandgap can be enlarged by increasing the strength of SOC. Resonant transmission has been found in the electronic bandgap, which is characterized by perfect transmission peak. Interestingly, by introducing a weak magnetic modulation, the transmission spectra of spin-up and spin-down electrons are separated. With increasing the length of the centre segment in the SSN, multiple spin-dependent perfect transmission peaks appear in the bandgap. The resonant energy and the number of modes of resonant transmission therein can be manipulated. Around resonant energy, high spin-polarization is observed, and fully spin-polarized conductance is obtained in this SSN. Our investigations achieve potential applications in spin filters.