Magnetothermoelectric transport properties of multiterminal graphene nanoribbons

摘要

The Peltier effect and the Ettingshausen effect are investigated in graphene nanoribbons, where charge current produces heat current along the longitudinal direction in the former case, and longitudinal charge current generates transverse heat current in the latter case. With the aid of the nonequilibrium Green's function and the Landauer-Buettiker formalism, the Peltier coefficient П_C and the Ettingshausen coefficient E_c are obtained. We found that the Kelvin relation is always valid for the longitudinal thermoelectric transport, i.e., П_c = TS_C, with T the temperature and S_c the Seebeck coefficient. In contrast, for transverse magnetothermoelectric transport, the Kelvin relation breaks down and E_c≠TN_C usually, with N_c the Nernst coefficient. In the region of weak magnetic field, the Ettingshausen effect depends strongly on device parameters. When the Fermi energy E_F is close to the Dirac point, the Ettingshausen effect of the semiconducting armchair graphene nanoribbon is much stronger than that of the metallic one. When E_F is far away from the Dirac point, the Ettingshausen coefficient E_c oscillates around zero. When under a strong magnetic field, Er is independent of the device parameters and swells only near the Dirac point. Further, the dependence of Ec on EF can be scaled by E_F/k_BT, with a peak value of (2n2)k_BT/e for the three-terminal system and (4/3 In2)k_BT/e for the four-terminal system. We also study the impact of disorder on the Ettingshausen effect. Regardless of the magnetic field strength, E_c is robust against moderate disorder scattering. In addition, in the strong magnetic field, E_c with additional regular oscillating structure can be caused by disorder.