  A new type of blockade effect - spin-orbit blockade (SOB) - is found in the
conduction of a quantum dot (QD) made of a material with spin-orbit
interaction. The blockade arises from spin-filtering effect in a quantum point
contact (QPC), which is a component of the QD. Hence the appearance of the
blockade itself evidences the spin-filtering effect in the QPC. The lower bound
of filtering efficiency is estimated to be above 80%.
