Experimental Spin Ratchet
  Spintronics relies on the ability to transport and utilize the spin properties of an electron rather than its charge. We describe a spin rachet at the single-electron level that produces spin currents with no net bias or charge transport. Our device is based on the ground state energetics of a single electron transistor comprising a superconducting island connected to normal leads via tunnel barriers with different resistances that break spatial symmetry. We demonstrate spin transport and quantify the spin ratchet efficiency using ferromagnetic leads with known spin polarization. Our results are modeled theoretically and provide a robust route to the generation and manipulation of pure spin currents. 
Marius V. Costache and Sergio O. Valenzuela
cond-mat.mes-hall cond-mat.supr-con