Universal Thermoelectric Effect of Dirac Fermions in Graphene

TL;DR

This study numerically investigates the thermoelectric properties of Dirac fermions in graphene under strong magnetic fields and disorder, revealing universal behaviors and validating theoretical relations with experimental relevance.

Contribution

It uncovers universal thermoelectric behaviors in graphene's Dirac fermions and confirms the generalized Mott relation across various temperatures.

Findings

Transverse thermoelectric conductivity reaches a universal quantum value at LL centers.

Nernst signal peaks at LL centers with heights around $k_B/e$ and changes sign elsewhere.

Thermopower exhibits opposite behavior to Nernst signal, aligning with experimental data.

Abstract

We numerically study the thermoelectric transports of Dirac fermions in graphene in the presence of a strong magnetic field and disorder. We find that the thermoelectric transport coefficients demonstrate universal behavior depending on the ratio between the temperature and the width of the disorder-broadened Landau levels(LLs). The transverse thermoelectric conductivity $\alpha_{xy}$ reaches a universal quantum value at the center of each LL in the high temperature regime, and it has a linear temperature dependence at low temperatures. The calculated Nernst signal has a peak at the central LL with heights of the order of $k_B/e$, and changes sign near other LLs, while the thermopower has an opposite behavior, in good agreement with experimental data. The validity of the generalized Mott relation between the thermoelectric and electrical transport coefficients is verified in a wide range of temperatures.