Spin Thermoelectric Transport Properties In Mesoscopic Quantum Dot Systems

In this paper, mesoscopic quantum dot(QD) systems are designed theoretically.And by using the non-equilibrium Green’s function, the spin thermoelectric properties were thoroughly studied in these structures. Some novel spin dependent transport properties and the potential application were found, which provides a physical the model and theoretical basis for the design of a new type of thermoelectric devices.In an AB ring QD system weakly coupled in metal electrodes, we found that by applying an external thermal bias to QD-1, the spin Seebeck e?ect can be induced due to the presence of Heisenberg exchange coupling without the need for any extra magnetic field or ferromagnetic electrodes, which can be manipulated e?ectively by the spin-orbit interaction(RSOI) and magnetic flux.In an AB ring with an embedded magnetic impurity quantum dot system, due to the exchange coupling between the impurity and the electrons in QD, a significant spin output power and e?ciency are obtained. Both the magnitude and polarization direction of that can be e?ectively modulated by adjusting the gate voltage. The interference term in the AB ring can be manipulated by the RSOI and magnetic flux, and thus the spin e?ciency shows a Zig-zag pattern, which can be used for an on/o? switch to the thermoelectric current.In a four-terminal four-QD ring structure, with the assistance of RSOI, the pure spin Nernst e?ect can occur by applying a thermal bias; Under certain RSOI and magnetic field strength, fully-polarized currents can be driven from terminal 2 or 4, of which the sign and the magnitude can be modulated by adjusting the RSOI-induced phase factor and the magnetic flux. Moreover, the magnitude of the Nernst e?ect can be remarkably enhanced by the intra-dot Coulomb blockade, the Nernst coe?cient is predicted to be more than two times larger than the case of zero Coulomb interaction.In a pair of vertically aligned quantum dots system attached to four leads, the sign and the magnitude of Nernst coe?cient can be modulated by the relative magnetic configuration and polarization strength of ferromagnetic(FM) electrodes. When the magnetic moments in the 1 and 3 electrodes are turned to antiparallel alignment, the pure spin Nernst(without charge Nernst) e?ect can occur by applying a transverse thermal bias. As the lead 4 transition from metal to ferromagnet, both the spin and charge Nernst e?ects can be obtained simultaneously. Moreover, the magnitude of the Nernst e?ect can be remarkably enhanced by the intra-dot and inter-dot Coulomb repulsion. The Nernst coe?cient is predicted to be more than 100 times larger than the case of zero Coulomb interaction.