  Thermoelectric effects in a double quantum dot system coupled to external
magnetic/nonmagnetic leads are investigated theoretically. The basic
thermoelectric transport characteristics, like thermopower, electronic
contribution to heat conductance, and the corresponding figure of merit, have
been calculated in terms of the linear response theory and Green function
formalism in the Hartree-Fock approximation for Coulomb interactions. An
enhancement of the thermal efficiency (figure of merit ZT) due to Coulomb
blockade has been found. The magnitude of ZT is further considerably enhanced
by quantum interference effects. Both the Coulomb correlations and interference
effects lead to strong violation of the Wiedemann-Franz law. The influence of
spin-dependent transport and spin bias on the thermoelectric effects
(especially on Seebeck and spin Seebeck effects) is also analyzed.
