Abstract
We investigate spin currents and spin-current correlations for double quantum dots in the spin blockade regime. By analysing the time evolution of the density matrix, we obtain the spin resolved currents and derive from a generating function an expression for the fluctuations and correlations. Both the charge current and the spin current turn out to be generally super-Poissonian. Moreover, we study the influence of ac fields acting upon the transported electrons. In particular, we focus on fields that cause spin rotation or photon-assisted tunnelling.
Highlights
We consider two weakly coupled quantum dots connected to two fermionic leads described by the Hamiltonian
The contribution of these two effects—single electron spin resonance and the suspension of channel blocking by singlet–triplet mixing—results in a non-monotonic dependence of the Fano factor, which is considerably enhanced in the vicinity of the degenerate Zeeman splitting
We have studied the suspension of spin blockade in the electron transport through coherently coupled double quantum dots by ac-driving fields, thermal excitations and spin-flip scattering
Summary
We consider two weakly coupled quantum dots connected to two fermionic leads (cf figure 1) described by the Hamiltonian. Where H 0 = iσ εiσ ci†σ ciσ + i Ui ni↑ni↓ + ULRn Ln R describes the two isolated quantum dots, H LR = − σ (tLRcL†σ cRσ + h.c.) is the inter-dot coupling. The current is quenched whenever the electrons in each quantum dot have the same spin polarization and the Pauli exclusion principle avoids inter-dot tunnelling [12]. The o√ccupation of any inter-dot triplet state, |+ = |↑,↑ , |− = |↓, ↓ and |T0 = (|↑, ↓ + |↓, ↑ )/ 2 inhibits the transport to the collector [10], unless, as we will discuss below, the singlet and the triplet subspace mix due to any perturbation, as for instance an inhomogeneous magnetic field in the sample, which produces different Zeeman splittings within each quantum dot
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