Magnetothermoelectric transport properties in graphene superlattices with one-dimensional periodic potentials

We numerically study the thermoelectric transport in graphene superlattice in the presence of a strong magnetic field and disorder, with a one-dimensional periodic potential barrier oriented along the armchair direction of graphene. The thermoelectric coefficients exhibit novel properties as functions of the superlattice period length. When the period length is taken to be the smallest, we find that the thermoelectric transport exhibits properties similar to those in the absence of the superlattice potential. The thermoelectric conductivities display different asymptotic behaviors, depending on the ratio between the temperature and the width of the disorder-broadened Landau levels ( LLs). In the high-temperature regime, the transverse thermoelectric conductivity alpha(xy) saturates to a universal value 2.27k(B)e/h at the center of each LL, and displays a linear temperature dependence at low temperatures. We attribute this unique behavior to the coexistence of particle and hole LLs. Both the Nernst signal and the thermopower show a large peak around the central LL. However, with increasing the superlattice period length, it is found that the thermoelectric transport properties are consistent with the behavior of a band insulator. alpha(xy) displays a pronounced valley at low temperatures. This behavior can be understood as due to the split of the valley degeneracy in the central LL. The obtained results demonstrate the sensitivity of the thermoelectric conductivity to the superlattice period length. Copyright (C) EPLA, 2015