Tunable spin-diode with a quantum dot coupled to leads

Spin-dependent electronic transport through a quantum dot coupled to one ferromagnetic lead and one normal metal lead is investigated by using the master equation approach. Both the intradot spin-flip transition and Coulomb interaction are studied for the current polarization p = (I-up arrow - I-down arrow)/(I-up arrow + I-down arrow). It is found that p is suppressed to zero for a particular regime of one direction bias, while it is enhanced to a relative maximum value when the bias is reversed, which is called the spin- current diode effect. The bias regime of this effect is determined by the dot level position and the intradot Coulomb interaction strength. We give a physical explanation and several control methods for it. This device is realizable with current nanofabrication technology and should have practical applications in spintronics.