We study the coexistence of the spin-polarized current and the spin accumulation in a three-terminal quantum ring structure, in which two quantum dots (QDs) are inserted in one arm of the ring and the Rashba spin-orbit interaction (RSOI) exists in the other. We find that by properly adjusting the applied voltages in the three leads, the RSOI-induced phase factor and the parameters relevant to the QDs, the spin-polarization efficiency in the leads can achieve either 100% or infinite, and the electrons of the same or different spin directions can accumulate in the two dots, respectively. The manipulation of the electron spin in the present device relies on the RSOI and the electric fields, thus making it realizable with the currently existing technologies.
We theoretically study the heat generation in a quantum dot (QD) connected simultaneously to two reservoirs and a local phonon bath. We find that driven solely by an external thermal bias, the resonant tunneling electrons can absorb heat from the phonon bath to the QD that are held at the same temperature. This QD refrigerator also works well under the thermoelectric effect. At room temperature and large thermal bias, the magnitude of the heat current density is on the order of nW/cm2 in typical Ge/Si QD, of which the dot diameter is 40 nm with phonon frequency 5 × 1013 rad/s.
The spin thermoelectric effects are studied in a Rashba double quantum dot (QD) attached to ferromagnetic leads with noncollinear magnetic moments. The spin conductance G(s), spin thermopower S(s), electron thermal conductance κ(el) and spin thermoelectric figure of merit Z(s)T are calculated by using Green's function method. We find that the magnitude of the spin figure of merit can be remarkably enhanced by the coexistence of the Rashba spin-orbit interaction in the QDs and the leads' spin polarization, and can reach even as high as 3 by optimizing the parameters of the structure. The angle between the leads' magnetic moments can act as a powerful means to manipulate the properties of the spin figure of merit.
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