Interaction driven giant thermopower in magic-angle twisted bilayer graphene

TL;DR

This study measures thermopower in magic-angle twisted bilayer graphene, revealing giant, peak-like thermopower features linked to particle-hole asymmetry and superconducting fluctuations, challenging conventional theoretical expectations.

Contribution

It provides the first detailed thermopower measurements in MtBLG, uncovering large thermopower peaks and their relation to electronic structure and superconducting phenomena.

Findings

Thermopower reaches up to 100 μV/K at 1K.

Peak-like thermopower features correlate with resistance peaks at Moire fillings.

Anomalous thermopower peak observed near superconducting transition.

Abstract

Magic-angle twisted bilayer graphene (MtBLG) has proven to be an extremely promising new platform to realize and study a host of emergent quantum phases arising from the strong correlations in its narrow bandwidth flat band. In this regard, thermal transport phenomena like thermopower, in addition to being coveted technologically, is also sensitive to the particle-hole (PH) asymmetry, making it a crucial tool to probe the underlying electronic structure of this material. We have carried out thermopower measurements of MtBLG as a function of carrier density, temperature and magnetic field, and report the observation of an unusually large thermopower reaching up to a value as high as $\sim \bf{100\mu V/K}$ at a low temperature of 1K. Surprisingly, our observed thermopower exhibiting peak-like features in close correspondence to the resistance peaks around the integer Moire fillings, including the Dirac Point, violating the Mott formula. %Surprisingly, our observed thermopower exhibits peak-like features in close correspondence to the resistance peaks around the integer Moire fillings, including the Dirac Point, which completely violates the Mott formula. We show that the large thermopower peaks and their %non-monotonic dependence with temperature and magnetic field associated behaviour arise from the emergent highly PH asymmetric electronic structure due to the cascade of Dirac revivals. Furthermore, the thermopower shows an anomalous peak around the superconducting transition on the hole side and points towards the possible role of enhanced superconducting fluctuations in MtBLG.