Remote-control spin filtering through a $T$-type structure
  We propose a spin filter scheme using a $T$-stub waveguide. By applying a moderate magnetic field at the tip of the sidearm, this device can produce both large electric and spin current. The direction, polarization of the output spin current can be further adjusted electronically by a remote gate which tunes the length of the sidearm. The device is robust against the disorder. 
X. Y. Feng, J. H. Jiang, M. Q. Weng