Interaction-driven giant thermopower in magic-angle twisted bilayer graphene

Magic-angle twisted bilayer graphene has proved to be a fascinating platform to realize and study emergent quantum phases arising from the strong correlations in its flat bands. Thermal transport phenomena, such as thermopower, are sensitive to the particle-hole asymmetry, making them a crucial tool to probe the underlying electronic structure of this material. Here we have carried out thermopower measurements of magic-angle twisted bilayer graphene as a function of carrier density, temperature and magnetic field. We report the observation of an unusually large thermopower reaching a value of the order of 100 mu V K-1 at a low temperature of 1 K. The thermopower exhibits peak-like features that violate the Mott formula in close correspondence to the resistance peaks appearing around the integer filling of the moire bands, including the Dirac point. We show that the large thermopower peaks and their associated behaviour arise from the emergent highly particle-hole-asymmetric electronic structure, due to the sequential filling of the moire flat bands and the associated recovery of Dirac-like physics. Furthermore, the thermopower shows an anomalous peak around the superconducting transition, which points towards the possible role of superconducting fluctuations in magic-angle twisted bilayer graphene. Thermal transport measurements provide a complementary view of the electronic structure of a material to electronic transport. This technique is applied to twisted bilayer graphene, and highlights the particle-hole asymmetry of its band structure.