Enhanced Spin Figure of Merit in a Molecular Junction

We study the spin-dependent thermoelectric effect in a molecular junction where a semiconductor quantum dot in a magnetic field is trapped between two conducting polymer leads. The Green’s function method along with the Landauer formula based on the Holstein small polaron model is applied to study the thermo-spin effects in this system. The narrow bandwidth of the small polaron band in the polymer leads results in sharp carrier density of states, which offers the opportunity to enhance the spin Seebeck coefficient. At the same time, the spin conductance and electron thermal conductance can be tuned by tuning the affinity mismatch and chemical potential flexibly. Consequently, significant enhancement of spin figure of merit can be achieved. Detailed calculation of the influence of band mismatch, width of a small polaron band, chemical potential, temperature, and magnetic field on the thermo-spin effects is shown in this work. Our results show that the value of spin figure of merit is larger than 1 at a wide parameter range. Specially, the spin figure of merit can be up to 9 when the band mismatch is 0.52 eV and the coupling strength is 5 meV at room temperature. This work indicates that the efficient generation and control of spin polarization can be realized in the polymer–semiconductor–polymer hybrid nanoscale structure.