Enhancement of charge and spin Seebeck effect in triple quantum dots coupling to ferromagnetic and superconducting electrodes

Highlights: • The gap suppresses thermal conductance and enhances thermopower, and improves figure of merit in F-TQD-S system. • The interdot tunneling splitting scheme provides a way of controlling charge figure of merit by external magnetic field. • The interdot tunneling coupling greatly enhances charge figure of merit in F-TQD-S system compared to F-QD-S system. • The spin polarization of electrode and interdot tunneling splitting can improve spin thermopower and spin figure of merit. - Abstract: We theoretically study the thermoelectric transport properties through a triple quantum dots (QDs) device with the central QD coupled to a ferromagnetic lead, a superconducting one, and two side QDs with spin-dependent interdot tunneling coupling. The thermoelectric coefficients are calculated in the linear response regime by means of nonequilibrium Green's function method. The thermopower is determined by the single-electron tunneling processes at the edge of superconducting gap. Near the outside of the gap edge the thermopower is enhanced while thermal conductance is suppressed, as a result, the charge figure of merit can be greatly improved as the gap appropriately increases. In the same way, charge figure of merit also can be greatly improved near the outside of the gap edge by adjusting interdot tunneling coupling and asymmetry coupling of the side QDs to central QD. Moreover, the appropriate increase of the interdot tunneling splitting and spin polarization of ferromagnetic lead not only can improve charge thermopower and charge figure of merit, but also can enhance spin thermopower and spin figure of merit. Especially, the interdot tunneling splitting scheme provides a method of controlling charge (spin) figure merit by external magnetic field.