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Theory of spin blockade, charge ratchet effect, and thermoelectrical behavior in serially coupled quantum-dot system
The charge transport of a serially coupled quantum dots (SCQD) connected to
the metallic electrodes is theoretically investigated in the Coulomb blockade
regime. A closed-form expression for the tunneling current of SCQD in the
{\color{red} weak interdot hopping} limit is obtained by solving an extended
two-site Hubbard model via the Green's function method. We use this expression
to investigate spin current rectification, negative differential conductance,
and coherent tunneling in the nonlinear response regime. The current
rectification arising from the space symmetry breaking of SCQD is suppressed by
increasing temperature. The calculation of SCQD is extended to the case of
multiple parallel SCQDs for studying the charge ratchet effect and SCQD with
multiple levels. In the linear response regime, the functionalities of spin
filter and low-temperature current filter are demonstrated to coexist in this
system. It is further demonstrated that two-electron spin singlet and triplet
states can be readily resolved from the measurement of Seebeck coefficient
rather than that of electrical conductance.Comment: 11 pages, 9 figures. Revised argument, results unchanged, added
reference
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