The thermopower and Nernst Effect in graphene in a magnetic field

We report measurements of the thermopower $S$ and Nernst signal $S_{yx}$ in graphene in a magnetic field $H$. Both quantities show strong quantum oscillations vs. the gate voltage $V_g$. Our measurements for Landau Levels of index $n\mathrm{\ne }0$ are in quantitative agreement with the edge-current model of Girvin and Jonson (GJ). The inferred off-diagonal thermoelectric conductivity ${\alpha }_{yx}$ comes close to the quantum of Amps per Kelvin. At the Dirac point ($n=0$), however, the width of the peak in ${\alpha }_{yx}$ is very narrow. We discuss features of the thermoelectric response at the Dirac point including the enhanced Nernst signal.