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, BZp(BZs)BZp(BZs) and the relative angle of these fields, θθ. If the effect of the Coulomb interaction can be neglected, we can expect to observe four resonant peaks when BZp≠BZsBZp≠BZs 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 BZp>BZsBZp>BZs, we always found a single resonant peak as a function of the energy offset. The peak current is maximum when θ=0θ=0 and decreases monotonically for a larger θ<π/2θ<π/2. In contrast, when BZpπ/4θ>π/4.