Thermoelectric transport for a quantum wire side-coupled to a graphene sheet between ferromagnetic leads

Abstract

We theoretically investigate the thermoelectric transport through a quantum wire (QW) side-coupled by a graphene sheet and sandwiched between two ferromagnetic electrodes with noncollinear magnetic moments. By using the nonequilibrium Green's function combining with the tight-binding Hamiltonian, it is demonstrated that both the thermopower and the electronic contribution to the thermal conductance develop an oscillating behavior with resonances and antiresonances due to constructive and destructive interferences in the system, respectively. Interestingly, the thermopower changes its sign for even- or odd-number of atoms in the wire, and the thermal conductance is always positive with an even-odd behavior at zero energy level position of the quantum wire. Moreover, the thermopower and the thermal conductance are weakly dependent on the wire–graphene coupling strength as well as the relative magnetic configurations of leads. On the contrary, they are both strongly dependent on the temperature and the polarization strength of the leads. The results obtained here may provide a valuable theoretical guidance to experimentally design heat spintronic devices.