Electron scattering and thermopower in twisted bilayer graphene

Twisted bilayer graphene (TBLG) with a small twist-angle is of particular interest because of its distinct energy band, where recent electrical transport experiments revealed van Hove singularities (VHSs), hybridization gaps, and correlation-induced behaviors. To better understand the effect of VHSs in TBLG, we perform transport experiments in this study. We observe that the temperature-dependent resistivity follows a power-law for carrier density between the main charge neutrality and hybridization gap. The evolution of the temperature exponent with carrier density shows a W-shaped dependence, with minima near the VHSs and maxima toward the hybridization gap. This W-shaped behavior could be attributed to different electron scattering mechanisms. We also study thermopower in TBLG, where we observe multiple sign changes in thermopower near VHSs at low temperatures. Our work may provide more information about the electronic structure and physical process in the TBLG system.