Transverse thermoelectric conductivity of bilayer graphene in the quantum Hall regime

Abstract

We performed electric and thermoelectric transport measurements of bilayer graphene in a magnetic field up to 15 T. The transverse thermoelectric conductivity ${\ensuremath{\alpha}}_{xy}$, determined from four transport coefficients, attains a peak value of ${\ensuremath{\alpha}}_{xy,\text{peak}}$ whenever chemical potential lies in the center of a Landau level. The temperature dependence of ${\ensuremath{\alpha}}_{xy,\text{peak}}$ is dictated by the disorder width ${W}_{\text{L}}$. For ${k}_{\text{B}}T/{W}_{\text{L}}\ensuremath{\le}0.2$, ${\ensuremath{\alpha}}_{xy,\text{peak}}$ is nominally linear in temperature, which gives ${\ensuremath{\alpha}}_{xy,\text{peak}}/T=0.19\ifmmode\pm\else\textpm\fi{}0.03\text{ }\text{nA}/{\text{K}}^{2}$ independent of the magnetic field, temperature, and Landau-level index. At ${k}_{\text{B}}T/{W}_{\text{L}}\ensuremath{\ge}0.5$, ${\ensuremath{\alpha}}_{xy,\text{peak}}$ saturates to a value close to the predicted universal value of $4\ifmmode\times\else\texttimes\fi{}(\text{ln}\text{ }2){k}_{\text{B}}e/h$ according to the theory of Girvin and Jonson. We remark that an anomaly is found in ${\ensuremath{\alpha}}_{xy}$ near the charge neutral point, similar to that in single-layer graphene.