Cotunneling through two-level quantum dots weakly coupled to ferromagnetic leadsI. Weymann
Department of Physics, Adam Mickiewicz University - 61-614 Poznan, Poland
received 13 July 2006; accepted in final form 27 October 2006
published online 23 November 2006
The spin-polarized transport through two-level quantum dots weakly coupled to ferromagnetic leads is considered theoretically in the Coulomb blockade regime. It is assumed that the dot is doubly occupied, so that the current flows due to cotunneling through singlet and triplet states of the dot. It is shown that transport characteristics strongly depend on the ground state of the quantum dot. If the ground state is a singlet, differential conductance (G) displays a broad minimum at low bias voltage, while tunnel magnetoresistance (TMR) is given by the Julliere value. If the ground state of the system is a triplet, there is a maximum in differential conductance at zero bias when the leads form the antiparallel configuration. The maximum is accompanied by a minimum in TMR. The different behavior of G and TMR may thus help to determine the ground state of the dot and the energy difference between the singlet and triplet states.
85.75.-d - Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields.
73.63.Kv - Quantum dots.
73.23.Hk - Coulomb blockade; single-electron tunneling.
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