We study electron transport through an Aharonov-Bohm ͑AB͒ interferometer with a noninteracting quantum dot in each of its arms. Both a magnetic flux threading through the AB ring and the Rashba spin-orbit ͑SO͒ interaction inside the two dots are taken into account. Due to the existence of the SO interaction, the electrons flowing through different arms of the AB ring will acquire a spin-dependent phase factor in the tunnel-coupling strengths. This phase factor, as well as the influence of the magnetic flux, will induce various interesting interference phenomena. We show that the conductance and the local density of states can become spin polarized by tuning the magnetic flux and the Rashba interaction strength. Under certain circumstances, a pure spin-up or spin-down conductance can be obtained when a spin-unpolarized current is injected from the external leads. Therefore, the electron spin can be manipulated by adjusting the Rashba spin-orbit strength and the structure parameters.

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.

Enhanced spin figure of merit in a Rashba quantum dot ring connected to ferromagnetic leadsWe propose a pure thermoelectric spin generator based on a Rashba quantum dot molecular junction by using the temperature difference instead of the usual voltage bias difference. A magnetic flux penetrating through the device is also considered. The spin Seebeck coefficient S S and the spin figure of merit Z S T of the molecular junction are calculated in terms of the Green's function formalism and the equation of motion (EOM) technique. It is found that a pure spin-up (spin-down) Seebeck coefficient can be generated by the coaction of the magnetic flux and the Rashba spin-orbit (RSO) interaction.

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.

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