Quantum spin transport in magnetic-field-engineered nano-structures

We theoretically investigated the resonant current that passes through a series coupled double quantum dots (QDs) subject to different Zeeman splittings under finite bias and strong Coulomb interaction conditions. When the Zeeman fields are different but collinear, there is always a single resonant peak. And when both Zeeman sub-levels of the QD near the source reservoir (probe QD) can be filled, we can expect the current to be strongly suppressed, which can be identified as a spin blockade. When the magnetic fields in each QD are non-collinear, we need to consider three parameters, the Zeeman energy in the probe (sample) dot, B-Zp(B-Zs) and the relative angle of these fields, 0. If the effect of the Coulomb interaction can be neglected, we can expect to observe four resonant peaks when B-Zp not equal B-Zs since the spin eigenstate in one QD has a finite tunnel matrix element with both spin eigenstates in the other QD. However, the Coulomb correlation modifies the result significantly. When B-Zp > B-Zs, we always found a single resonant peak as a function of the energy offset. The peak current is maximum when 0 = 0 and decreases monotonically for a larger 0 < pi/2. In contrast, when B-Zp < B-Zs, there were three peaks for 0 < pi/4 and two peaks for 0 > pi/4. (C) 2009 Elsevier B.V. All rights reserved.