Anomalous thermoelectric transport of Dirac particles in graphene

We report a thermoelectric transport property study of single layer graphene devices in both classical and quantum Hall regimes. In zero magnetic field, by sweeping the gate voltage V$_{g}$ to vary the carrier density $n_{2D} $, we demonstrate a diverging behavior in the Seebeck coefficient $S_{xx}$, i.e.$S_{xx} \sim 1/\sqrt {n_{2D} } $, which is a direct consequence of the linear energy dispersion of the massless particles. At low temperatures and high carrier densities, the Seebeck coefficient depends linearly on temperature, indicating the validity of the Mott relation. In the applied magnetic fields, we observe an anomalously large Nernst signal($\sim $ 6 $\mu $V/K*T) at the Dirac point. This is another unusual property expected for massless particles. At low temperatures where the quantum Hall effect is observed, both the Seebeck and Nernst signals show oscillations corresponding to the Landau levels manifested in the quantum Hall plateaus.