Evidence of compensated semimetal with electronic correlations at charge neutrality of twisted double bilayer graphene

Ayan Ghosh; Souvik Chakraborty; Unmesh Ghorai; Arup Kumar Paul; K. Watanabe; T. Taniguchi; Rajdeep Sensarma; Anindya Das

doi:10.1038/s42005-023-01480-x

Article Evidence of compensated semimetal with electronic correlations at charge neutrality of twisted double bilayer graphene

Ayan Ghosh ; Souvik Chakraborty ; Unmesh Ghorai ; Arup Kumar Paul ; K. Watanabe (National Institute for Materials Science) ; T. Taniguchi (National Institute for Materials Science) ; Rajdeep Sensarma ; Anindya Das

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Ayan Ghosh, Souvik Chakraborty, Unmesh Ghorai, Arup Kumar Paul, K. Watanabe, T. Taniguchi, Rajdeep Sensarma, Anindya Das. Evidence of compensated semimetal with electronic correlations at charge neutrality of twisted double bilayer graphene. Communications Physics. 2023, 6 (1), 360. https://doi.org/10.1038/s42005-023-01480-x

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Recently, magic-angle twisted bilayer graphene (MATBLG) has shown the emergence of various interaction-driven novel quantum phases at the commensurate fillings of the moire ́ superlattice, while the charge neutrality point (CNP) remains mostly a vanilla insulator. Here, we show an emerging phase of nearly compensated semimetallicity at the CNP of twisted double bilayer graphene (TDBLG), a close cousin of MATBLG, with a signature of strong correlation. Using electrical and thermal transport, we find almost two orders of magnitude enhancement of the thermopower in magnetic fields much smaller than the extreme quantum limit, accompanied by a large magnetore- sistance (∼ 2500%) at CNP. This provides indisputable experimental evidence that TDBLG near CNP is a compensated semimetal. Moreover, we observe a two-peak structure in the resistance variation with carrier density around the CNP and its unusual sublinear temperature dependence at low temperatures. The electronic correlations determine the fate of the co-existing small electron and hole pockets near the CNP of the semimetallic TDBLG. Our theory with the formation of excitonic metal explains the resistance feature and its unique sublinear temperature dependence.

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