Effect of intrinsic spin relaxation on the spin-dependent cotunneling   transport through quantum dots
  Spin-polarized transport through quantum dots is analyzed theoretically in the cotunneling regime. It is shown that the zero-bias anomaly, found recently in the antiparallel configuration, can also exist in the case when one electrode is magnetic while the other one is nonmagnetic. Physical mechanism of the anomaly is also discussed. It is demonstrated that intrinsic spin relaxation in the dot has a significant influence on the zero-bias maximum in the differential conductance -- the anomaly becomes enhanced by weak spin-flip scattering in the dot and then disappears in the limit of fast spin relaxation. Apart from this, inverse tunnel magnetoresistance has been found in the limit of fast intrinsic spin relaxation in the dot. The diode-like behavior of transport characteristics in the cotunneling regime has been found in the case of quantum dots asymmetrically coupled to the leads. This behavior may be enhanced by the spin-flip relaxation processes. 
Ireneusz Weymann and J\'ozef Barnas