Thermopower and Nernst effect in graphene in a magnetic field

Abstract

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 $n\ne 0$ are in quantitative agreement with the edge-current model of Girvin and Jonson (GJ). The inferred off-diagonal thermoelectric conductivity ${\alpha }_{xy}$ is consistent in magnitude with GJ’s prediction. At the Dirac point $\left(n=0\right)$, however, the width of the peak in ${\alpha }_{xy}$ is very narrow. We discuss the physical meaning of the peak width and the puzzle raised by ${\alpha }_{xy}$ for states at the Dirac point.