Effect of carrier mobility on magnetothermoelectric transport properties of graphene

With a method to systematically tune the mobility of the same graphene devices, we have investigated the dependence of magnetothermoelectric transport properties of graphene on the carrier mobility. In a zero magnetic field, we find that, as the mobility increases, the Seebeck coefficient S-xx exhibits a more pronounced diverging trend near the Dirac point. In an external magnetic field, regular oscillations in S-xx are identified corresponding to quantized Landau levels. Only in high-mobility states does an extra pair of peaks and dips in S-xx emerge near the Dirac point that persists, at least, to 150 K, and the sign of the peak/dip is reversed as the mobility increases. Based on the signatures in the electrical conductivity and the Hall conductance near the Dirac point, we argue that the extra peak/dip in S-xx is associated with an insulating behavior. Furthermore, the main Nernst coefficient peak increases linearly as the mobility increases. Our magnetothermoelectric transport results reflect the contrast in the electronic properties of graphene between low and high carrier mobility states.