Transverse Thermoelectric Conductivity of Bilayer Graphene in Quantum Hall Regime

TL;DR

This study measures the transverse thermoelectric conductivity of bilayer graphene in high magnetic fields, revealing temperature-dependent behavior and universal values near Landau levels, with anomalies near the charge neutral point.

Contribution

It provides the first detailed experimental characterization of $ meta_{xy}$ in bilayer graphene under quantum Hall conditions, confirming theoretical predictions and revealing new anomalies.

Findings

$ m meta_{xy}$ peaks at Landau levels with a linear temperature dependence at low $ m k_BT/W_L$

Universal value of $ meta_{xy}$ near $ m 4 imes(ln2)k_Be/h$ at higher $ m k_BT/W_L$

Anomaly observed in $ meta_{xy}$ near the charge neutral point

Abstract

We performed electric and thermoelectric transport measurements of bilayer graphene in a magnetic field up to 15 Tesla. The transverse thermoelectric conductivity $\rm\alpha_{xy}$, determined from four transport coefficients, attains a peak value of $\rm\alpha_{xy, peak}$ whenever chemical potential lies in the center of a Landau level. The temperature dependence of $\rm\alpha_{xy, peak}$ is dictated by the disorder width $\rm W_L$. For $\rm k_BT/W_L\leq$0.2, $\rm\alpha_{xy, peak}$ is nominally linear in temperature, which gives $\rm\alpha_{xy,peak}/T=0.19 \pm 0.03 n A/K^2$ independent of the magnetic field, temperature and Landau Level index. At $\rm k_BT/W_L\geq$0.5, $\rm\alpha_{xy, peak}$ saturates to a value close to the predicted universal value of $\rm 4\times(ln2)k_Be/h$ according to the theory of Girvin and Jonson. We remark that an anomaly is found in $\rm\alpha_{xy}$ near the charge neutral point, similar to that in single-layer graphene